Yep, it's #1 so far. All-time? Take a look at this game in 1966, where Art Shamsky came in during the top of the 8th inning as part of a double-switch when a reliever was called in. He hit a home run in the bottom of the inning to give his Reds a lead. Their bullpen coughed up a run in the top of the 9th, and then a go-ahead run in the 10th, so in the bottom of the 10th Shamsky launched another one to extend the game. The Pirates scored two more in the 11th, and Shamsky responded with a two-run shot to send it to the 12th. Only one Red reached base after that, so when the Pirates took the lead again in the 13th, the lead held up because Cardenas grounded into a game-ending DP, leaving Shamsky in the hole. WPA of 1.503, and like Kepler it was only a partial game's worth of work. And the team still lost! https://www.baseball-reference.com/boxes/CIN/CIN196608120.shtml PS. Then there's Jimmie Foxx's 1.307 WPA game, in a 18-17 barnburner. He went 6-for-9 plus a walk, including 3 HR. He played all 18 innings, and I guess that watered down his clutch numbers a bit. Shortstop Johnny Burnett had a .910 WPA for the opponents. No pitcher for either team had a positive WPA, unsurprisingly. (There were only 5 pitchers total!) https://www.baseball-reference.com/boxes/CLE/CLE193207100.shtml Our own Nelson Cruz ranks third all time with 1.220 for this game while he was with Baltimore. He went 4-for-5 with two homers and a triple, driving in every Oriole run in a 7-5 extra innings win. https://www.baseball-reference.com/boxes/TBA/TBA201409070.shtml