SECURITIES AND EXCHANGE COMMISSION	
Washington, D.C. 20549	
 	
SCHEDULE 13G	
 	
Under the Securities Exchange Act of 1934	
(Amendment No. __)*	
 	
Mosaic Acquisition Corp.	
(Name of Issuer)	
 	
Class A Ordinary Shares, par value $0.0001 per share	
(Title of Class of Securities)	
 	
G62848117**	
(CUSIP Number)	
 	
October 19, 2017	
(Date of Event Which Requires Filing of this Statement)	

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:	
 	
¨	Rule 13d-1(b)	
ý	Rule 13d-1(c)	
¨	Rule 13d-1(d)	
 	
(Page 1 of 12 Pages)	
 
______________________________
*The remainder of this cover page shall be filled out for a reporting person's initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter the disclosures provided in a prior cover page.
**The Class A Ordinary Shares have no CUSIP number. The CINS number for the units which include the Class A Ordinary Shares is G62848117.
The information required in the remainder of this cover page shall not be deemed to be "filed" for the purpose of Section 18 of the Securities Exchange Act of 1934 (" Act ") or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

CUSIP No. G62848117	13G	Page  2  of 12 Pages	
 
1	NAME OF REPORTING PERSON
Davidson Kempner Partners	
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP	(a) ¨
(b) ý	
3	SEC USE ONLY	
4	CITIZENSHIP OR PLACE OF ORGANIZATION
New York	
NUMBER OF
SHARES
BENEFICIALLY
OWNED BY
EACH
REPORTING
PERSON WITH:	5	SOLE VOTING POWER
0	
	6	SHARED VOTING POWER
364,400	
	7	SOLE DISPOSITIVE POWER
0	
	8	SHARED DISPOSITIVE POWER
364,400	
9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
364,400	
10	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES	¨	
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)
1.21%	
12	TYPE OF REPORTING PERSON
PN	

 

CUSIP No. G62848117	13G	Page  3  of 12 Pages	
 
1	NAME OF REPORTING PERSON
Davidson Kempner Institutional Partners, L.P.	
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP	(a) ¨
(b) ý	
3	SEC USE ONLY	
4	CITIZENSHIP OR PLACE OF ORGANIZATION
Delaware	
NUMBER OF
SHARES
BENEFICIALLY
OWNED BY
EACH
REPORTING
PERSON WITH:	5	SOLE VOTING POWER
0	
	6	SHARED VOTING POWER
773,600	
	7	SOLE DISPOSITIVE POWER
0	
	8	SHARED DISPOSITIVE POWER
773,600	
9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
773,600	
10	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES	¨	
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)
2.58%	
12	TYPE OF REPORTING PERSON
PN	

 

CUSIP No. G62848117	13G	Page  4  of 12 Pages	
 
1	NAME OF REPORTING PERSON
Davidson Kempner International, Ltd.	
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP	(a) ¨
(b) ý	
3	SEC USE ONLY	
4	CITIZENSHIP OR PLACE OF ORGANIZATION
British Virgin Islands	
NUMBER OF
SHARES
BENEFICIALLY
OWNED BY
EACH
REPORTING
PERSON WITH:	5	SOLE VOTING POWER
0	
	6	SHARED VOTING POWER
862,000	
	7	SOLE DISPOSITIVE POWER
0	
	8	SHARED DISPOSITIVE POWER
862,000	
9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
862,000	
10	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES	¨	
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)
2.87%	
12	TYPE OF REPORTING PERSON
CO	

 

CUSIP No. G62848117	13G	Page  5  of 12 Pages	
 
1	NAME OF REPORTING PERSON
Davidson Kempner Capital Management LP	
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP	(a) ¨
(b) ý	
3	SEC USE ONLY	
4	CITIZENSHIP OR PLACE OF ORGANIZATION
Delaware	
NUMBER OF
SHARES
BENEFICIALLY
OWNED BY
EACH
REPORTING
PERSON WITH:	5	SOLE VOTING POWER
0	
	6	SHARED VOTING POWER
2,000,000	
	7	SOLE DISPOSITIVE POWER
0	
	8	SHARED DISPOSITIVE POWER
2,000,000	
9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
2,000,000	
10	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES	¨	
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)
6.67%	
12	TYPE OF REPORTING PERSON
PN	

 

CUSIP No. G62848117	13G	Page  6  of 12 Pages	
 
1	NAME OF REPORTING PERSON
Thomas L. Kempner, Jr.	
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP	(a) ¨
(b) ý	
3	SEC USE ONLY	
4	CITIZENSHIP OR PLACE OF ORGANIZATION
United States	
NUMBER OF
SHARES
BENEFICIALLY
OWNED BY
EACH
REPORTING
PERSON WITH:	5	SOLE VOTING POWER
0	
	6	SHARED VOTING POWER
2,000,000	
	7	SOLE DISPOSITIVE POWER
0	
	8	SHARED DISPOSITIVE POWER
2,000,000	
9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
2,000,000	
10	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES	¨	
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)
6.67%	
12	TYPE OF REPORTING PERSON
IN	

 

CUSIP No. G62848117	13G	Page  7  of 12 Pages	
 
1	NAME OF REPORTING PERSON
Robert J. Brivio, Jr.	
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP	(a) ¨
(b) ý	
3	SEC USE ONLY	
4	CITIZENSHIP OR PLACE OF ORGANIZATION
United States	
NUMBER OF
SHARES
BENEFICIALLY
OWNED BY
EACH
REPORTING
PERSON WITH:	5	SOLE VOTING POWER
0	
	6	SHARED VOTING POWER
2,000,000	
	7	SOLE DISPOSITIVE POWER
0	
	8	SHARED DISPOSITIVE POWER
2,000,000	
9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
2,000,000	
10	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES	¨	
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)
6.67%	
12	TYPE OF REPORTING PERSON
IN	

 

CUSIP No. G62848117	13G	Page  8  of 12 Pages	

Item 1(a).	NAME OF ISSUER	
 	 	
 	Mosaic Acquisition Corp. (the " Issuer ")	
 
Item 1(b).	ADDRESS OF ISSUER'S PRINCIPAL EXECUTIVE OFFICES	
 	 	
 	375 Park Avenue, New York, New York 10152	
 
Item 2(a).	NAME OF PERSON FILING	
 	 	
 	This Statement is filed by each of the entities and persons listed below, all of whom together are referred to herein as the " Reporting Persons ":	
 	 	 	
 	(i)	Davidson Kempner Partners, a New York limited partnership (" DKP "). MHD Management Co., a New York limited partnership (" MHD "), is the general partner of DKP and MHD Management Co. GP, L.L.C., a Delaware limited liability company, is the general partner of MHD.  DKCM is responsible for the voting and investment decisions of DKP;	
 	 	 	
 	(ii)	Davidson Kempner Institutional Partners, L.P., a Delaware limited partnership (" DKIP "). Davidson Kempner Advisers Inc., a New York corporation, is the general partner of DKIP. DKCM is responsible for the voting and investment decisions of DKIP;	
 	 	 	
 	(iii)	Davidson Kempner International, Ltd., a British Virgin Islands business company (" DKIL ").  DKCM is the investment manager of DKIL and is responsible for the voting and investment decisions of DKIL;	
 	 	 	
 	(iv)	Davidson Kempner Capital Management LP, a Delaware limited partnership and a registered investment adviser with the U.S. Securities and Exchange Commission, acts as investment manager to each of DKP, DKIP and DKIL (" DKCM "). DKCM GP LLC, a Delaware limited liability company, is the general partner of DKCM.  The managing members of DKCM are Thomas L. Kempner, Jr., Robert J. Brivio, Jr., Eric P. Epstein, Anthony A. Yoseloff, Avram Z. Friedman, Conor Bastable, Morgan P. Blackwell, Shulamit Leviant, Patrick W. Dennis and Gabriel T. Schwartz; and	
 	 	 	
 	(v)	Messrs. Thomas L. Kempner, Jr. and Robert J. Brivio, Jr. through DKCM, are responsible for the voting and investment decisions relating to the securities held by DKP, DKIP and DKIL reported herein.  	
 
Item 2(b).	ADDRESS OF PRINCIPAL BUSINESS OFFICE OR, IF NONE, RESIDENCE	
 	 	
 	The address of the principal business office of each of the Reporting Persons is c/o Davidson Kempner Capital Management LP, 520 Madison Avenue, 30th Floor, New York, New York 10022.	
 
Item 2(c).	CITIZENSHIP	
 	 	
 	(i)	DKP – a New York limited partnership	

CUSIP No. G62848117	13G	Page  9  of 12 Pages	
 
 	(ii)	DKIP – a Delaware limited partnership	
 	 	
 	(iii)	DKIL – a British Virgin Islands business company	
 	 	
 	(iv)	DKCM – a Delaware limited partnership	
 	 	
 	(v)	Messrs. Thomas L. Kempner, Jr. and Robert J. Brivio, Jr. – United States	
 
Item 2(d).	TITLE OF CLASS OF SECURITIES	
 	 	
 	Class A Ordinary Shares, par value $0.0001 per share (the " Class A Ordinary Shares ")	
 
Item 2(e).	CUSIP NUMBER	
 	 	
 	The Class A Ordinary Shares have no CUSIP number. The CINS number for the units which include the Class A Ordinary Shares is G62848117.	
 
Item 3.	IF THIS STATEMENT IS FILED PURSUANT TO Rules 13d-1(b), OR 13d-2(b) OR (c), CHECK WHETHER THE PERSON FILING IS A:	
 
 	(a)	¨	Broker or dealer registered under Section 15 of the Act;	
 	(b)	¨	Bank as defined in Section 3(a)(6) of the Act;	
 	(c)	¨	Insurance company as defined in Section 3(a)(19) of the Act;	
 	(d)	¨	Investment company registered under Section 8 of the Investment Company Act of 1940;	
 	(e)	¨	An investment adviser in accordance with Rule 13d-1(b)(1)(ii)(E);	
 	(f)	¨	An employee benefit plan or endowment fund in accordance with Rule 13d-1(b)(1)(ii)(F);
 	
 	(g)	¨	A parent holding company or control person in accordance with Rule 13d-1(b)(1)(ii)(G);	
 	(h)	¨	A savings association as defined in Section 3(b) of the Federal Deposit Insurance Act;
 	
 	(i)	¨	A church plan that is excluded from the definition of an investment company under Section 3(c)(14) of the Investment Company Act;
 	
 	(j)	¨	A non-U.S. institution in accordance with Rule 13d-1(b)(1)(ii)(J);	
 	(k)	¨	Group, in accordance with Rule 13d-1(b)(1)(ii)(K).	
 
 	If filing as a non-U.S. institution in accordance with Rule 13d-1(b)(1)(ii)(J), please
specify the type of institution:_____________________	

CUSIP No. G62848117	13G	Page  10  of 12 Pages	
 
Item 4.	OWNERSHIP .	
 	
 	The information required by Items 4(a) – (c) is set forth in Rows (5) – (11) of the cover page for each Reporting Person hereto and is incorporated herein by reference for each such Reporting Person.	
 	
 	The percentages used in this Schedule 13G are calculated based upon the 30,000,000 Class A Ordinary Shares reported to be outstanding in the Issuer's Prospectus filed pursuant to Rule 424(b)(4), filed with the Securities and Exchange Commission on October 19, 2017 after giving effect to the completion of the offering, as described therein.	
 
Item 5.	OWNERSHIP OF FIVE PERCENT OR LESS OF A CLASS	
 	 	
 	Not applicable.	
 
Item 6.	OWNERSHIP OF MORE THAN FIVE PERCENT ON BEHALF OF ANOTHER PERSON	
 	 	
 	Not applicable.	
 
Item 7.	IDENTIFICATION AND CLASSIFICATION OF THE SUBSIDIARY WHICH ACQUIRED THE SECURITY BEING REPORTED ON BY THE PARENT HOLDING COMPANY OR CONTROL PERSON	
 	 	
 	Not applicable.	
 
Item 8.	IDENTIFICATION AND CLASSIFICATION OF MEMBERS OF THE GROUP	
 	 	
 	Not applicable.	
 
Item 9.	NOTICE OF DISSOLUTION OF GROUP	
 	 	
 	Not applicable.	
 
Item 10.	CERTIFICATION	
 
 	Each of the Reporting Persons hereby makes the following certification:	
 	 	
 	By signing below each Reporting Person certifies that, to the best of his or its knowledge and belief, the securities referred to above were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect.	

CUSIP No. G62848117	13G	Page  11  of 12 Pages	
SIGNATURES
After reasonable inquiry and to the best of his or its knowledge and belief, each of the undersigned certifies that the information set forth in this statement is true, complete and correct.
DATE: October 30, 2017
 
 	DAVIDSON KEMPNER PARTNERS	
 	By: MHD Management Co.,	
 	its General Partner	
 	 	
 	By: MHD Management Co. GP, L.L.C.,	
 	its General Partner	
 	 	
 	/s/ Thomas L. Kempner, Jr. 	
 	Name:  Thomas L. Kempner, Jr.	
 	Title:    Executive Managing Member	
 	 	
 	DAVIDSON KEMPNER INSTITUTIONAL PARTNERS, L.P.	
 	By: Davidson Kempner Advisers Inc.,	
 	its General Partner	
 	 	
 	/s/ Thomas L. Kempner, Jr. 	
 	Name:  Thomas L. Kempner, Jr.	
 	Title:    President	
 	 	
 	DAVIDSON KEMPNER INTERNATIONAL, LTD.	
 	By: Davidson Kempner Capital Management LP,	
 	its Investment Manager	
 	 	
 	/s/ Thomas L. Kempner, Jr. 	
 	Name:  Thomas L. Kempner, Jr.	
 	Title:    Executive Managing Member	
 	 	
 	DAVIDSON KEMPNER CAPITAL MANAGEMENT LP	
 	 	
 	/s/ Thomas L. Kempner, Jr. 	
 	Name:  Thomas L. Kempner, Jr.	
 	Title:    Executive Managing Member	
 	 	
 	/s/ Thomas L. Kempner, Jr. 	
 	THOMAS L. KEMPNER, JR.	
 	 	
 	/s/  Robert J. Brivio, Jr. 	
 	ROBERT J. BRIVIO, JR.	

 	 	

CUSIP No. G62848117	13G	Page  12  of 12 Pages	
JOINT FILING AGREEMENT
PURSUANT TO RULE 13d-1(k)
The undersigned acknowledge and agree that the foregoing statement on Schedule 13G is filed on behalf of each of the undersigned and that all subsequent amendments to this statement on Schedule 13G shall be filed on behalf of each of the undersigned without the necessity of filing additional joint filing agreements. The undersigned acknowledge that each shall be responsible for the timely filing of such amendments, and for the completeness and accuracy of the information concerning him or it contained herein and therein, but shall not be responsible for the completeness and accuracy of the information concerning the others, except to the extent that he or it knows or has reason to believe that such information is inaccurate.
DATE: October 30, 2017

 	DAVIDSON KEMPNER PARTNERS	
 	By: MHD Management Co.,	
 	its General Partner	
 	 	
 	By: MHD Management Co. GP, L.L.C.,	
 	its General Partner	
 	 	
 	/s/ Thomas L. Kempner, Jr. 	
 	Name:  Thomas L. Kempner, Jr.	
 	Title:    Executive Managing Member	
 	 	
 	DAVIDSON KEMPNER INSTITUTIONAL PARTNERS, L.P.	
 	By: Davidson Kempner Advisers Inc.,	
 	its General Partner	
 	 	
 	/s/ Thomas L. Kempner, Jr. 	
 	Name:  Thomas L. Kempner, Jr.	
 	Title:    President	
 	 	
 	DAVIDSON KEMPNER INTERNATIONAL, LTD.	
 	By: Davidson Kempner Capital Management LP,	
 	its Investment Manager	
 	 	
 	/s/ Thomas L. Kempner, Jr. 	
 	Name:  Thomas L. Kempner, Jr.	
 	Title:    Executive Managing Member	
 	 	
 	DAVIDSON KEMPNER CAPITAL MANAGEMENT LP	
 	 	
 	/s/ Thomas L. Kempner, Jr. 	
 	Name:  Thomas L. Kempner, Jr.	
 	Title:    Executive Managing Member	
 	 	
 	/s/ Thomas L. Kempner, Jr. 	
 	THOMAS L. KEMPNER, JR.	
 	 	
 	/s/  Robert J. Brivio, Jr. 	
 	ROBERT J. BRIVIO, JR.