Roger Clemens has the highest Game Score in a postseason game, with a Game Score of 98 in Game 4 of the 2000 ALCS versus the Mariners.

Interpreted as:

biggest playoff game score by a player difference

	NAME	GSC	DATE	TM		OPP	DEC	GS	ERA	SO	CG	SHO	SV	IP	H	ER	R	HR	BB	HBP	GF	IBB	TBF	WP
1	Roger Clemens R. Clemens	98	10/14/2000	NYY	@	SEA	W	1	0.00	15	1	1	0	9.0	1	0	0	0	2	0	0	0	30	0
2	Dave McNally D. McNally	97	10/5/1969	BAL	vs	MIN	W	1	0.00	11	1	1	0	11.0	3	0	0	0	5	0	0	0	41	0
3	Babe Ruth B. Ruth	97	10/9/1916	BSA	vs	BKN	W	1	0.64	4	1	0	0	14.0	6	1	1	1	3	0	0	0	48	0
4	Tim Lincecum T. Lincecum	96	10/7/2010	SFG	vs	ATL	W	1	0.00	14	1	1	0	9.0	2	0	0	0	1	0	0	0	30	0
5	Roy Halladay R. Halladay	94	10/6/2010	PHI	vs	CIN	W	1	0.00	8	1	1	0	9.0	0	0	0	0	1	0	0	0	28	0
6	Don Larsen D. Larsen	94	10/8/1956	NYY	vs	BKN	W	1	0.00	7	1	1	0	9.0	0	0	0	0	0	0	0	0	27	0
7	Ed Walsh E. Walsh	94	10/11/1906	CWS	@	CHC	W	1	0.00	12	1	1	0	9.0	2	0	0	0	1	0	0	0	30	1
8	Josh Beckett J. Beckett	93	10/12/2003	FLA	vs	CHC	W	1	0.00	11	1	1	0	9.0	2	0	0	0	1	0	0	0	30	0
9	Ken Holtzman K. Holtzman	93	10/9/1973	OAK	vs	BAL	W	1	0.82	7	1	0	0	11.0	3	1	1	1	1	0	0	0	38	0
10	Bob Gibson B. Gibson	93	10/2/1968	STL	vs	DET	W	1	0.00	17	1	1	0	9.0	5	0	0	0	1	0	0	0	32	0
11	Kevin Brown K. Brown	92	9/29/1998	SDP	@	HOU	W	1	0.00	16	0	0	0	8.0	2	0	0	0	2	1	0	0	28	0
12	Randy Johnson R. Johnson	91	10/28/2001	ARI	vs	NYY	W	1	0.00	11	1	1	0	9.0	3	0	0	0	1	0	0	0	30	0
13	Randy Johnson R. Johnson	91	10/16/2001	ARI	vs	ATL	W	1	0.00	11	1	1	0	9.0	3	0	0	0	1	0	0	0	31	0
14	Cliff Lee C. Lee	90	10/18/2010	TEX	@	NYY	W	1	0.00	13	0	0	0	8.0	2	0	0	0	1	0	0	0	27	0
15	Livan Hernandez L. Hernandez	90	10/12/1997	FLA	vs	ATL	W	1	1.00	15	1	0	0	9.0	3	1	1	1	2	0	0	0	31	0
16	Nolan Ryan N. Ryan	90	10/14/1986	HOU	@	NYM		1	1.00	12	0	0	0	9.0	2	1	1	1	1	0	0	0	30	0
17	Mike Scott M. Scott	90	10/8/1986	HOU	vs	NYM	W	1	0.00	14	1	1	0	9.0	5	0	0	0	1	0	0	0	34	0
18	Vida Blue V. Blue	90	10/8/1974	OAK	@	BAL	W	1	0.00	7	1	1	0	9.0	2	0	0	0	0	0	0	0	30	0
19	Monte Pearson M. Pearson	90	10/5/1939	NYY	vs	CIN	W	1	0.00	8	1	1	0	9.0	2	0	0	0	1	0	0	0	29	0
20	George Earnshaw G. Earnshaw	90	10/6/1931	PHA	vs	SLN	W	1	0.00	8	1	1	0	9.0	2	0	0	0	1	0	0	0	30	0
21	Bill Dinneen B. Dinneen	90	10/2/1903	BSA	vs	PIT	W	1	0.00	11	1	1	0	9.0	3	0	0	0	2	0	0	0	29	0
22	Justin Verlander J. Verlander	89	10/11/2012	DET	@	OAK	W	1	0.00	11	1	1	0	9.0	4	0	0	0	1	0	0	0	31	0
23	Curt Schilling C. Schilling	89	10/9/2001	ARI	vs	STL	W	1	0.00	9	1	1	0	9.0	3	0	0	0	1	0	0	0	32	0
24	Kevin Millwood K. Millwood	89	10/6/1999	ATL	vs	HOU	W	1	1.00	8	1	0	0	9.0	1	1	1	1	0	0	0	0	29	0
25	Kevin Brown K. Brown	89	10/8/1998	SDP	@	ATL	W	1	0.00	11	1	1	0	9.0	3	0	0	0	3	0	0	0	32	1