The outfielder hit his fifth career grand slam in the Mets' five-run first inning and New York earned a three-game series sweep over the Miami Marlins with a 5-1 win on Sunday.
"It didn't feel any different — that was the weird part. My first start in a week or whatever it's been, but I've done this a million times, it wasn't really that awkward," said Bay, from Trail, B.C.
Chris Young (4-7) allowed one run and five hits in five innings. He walked one and struck out three as the Mets won for the seventh time in eight games.
The Mets wasted little time in getting to Mark Buehrle (12-12).
Ronny Cedeno led off the game with a double to deep centre field and took third on Justin Turner's double. Turner hit a fly down the right-field line, where the ball landed just inside fair territory as right-fielder Mike Stanton overran it.
Cedeno scored on David Wright's groundout. Following Scott Hairston's pop out, Buehrle walked Ike Davis and hit Kelly Shoppach with a pitch to load the bases.
Bay then drilled a 1-0 pitch into the right-centre-field seats for his seventh home run. He went 2 for 4 and raised his average to .160 with 18 RBIs.
"I was just thrilled for Jason. To come out and hit that ball early, with the struggles he's had, serious injuries he's faced. It was his win today," Young said.
Now in the third year of a guaranteed four-year, $66 million contract, Bay has been reduced to a platoon player. He has played in 55 games this season, and has spent two stints (concussion, fractured rib) on the disabled list.
"I'm not out there trying to impress anybody or fake anything," Bay said. "It's obviously been a very trying time, and I take a lot of pride trying to be the same guy every day."
His approach has earned him respect, even if he hasn't been the star he was brought in to be.
"This guy's a professional," Mets manager Terry Collins said. "He understands. He's the first guy to stand up and say, 'Look, I'm not getting it done. I don't blame you for what's going on. I got nobody to blame but myself,'"
Buehrle gave up five runs and six hits in seven innings. He walked one, struck out three and hit a batter.
Justin Ruggiano's two-out double in the fifth scored Rob Brantly with Miami's run. Brantly had walked and took second on Buehrle's sacrifice bunt.
Miami has dropped four in a row and eight of 10.
NOTES: The Mets swept the Marlins on the road for the first time since May 25-27, 2007. New York also swept Miami at Citi Field earlier this year (April 24-26). . Six of Bay's seven homers have been hit on the road. . Miami recalled RHP Tom Koehler and LHP Dan Jennings from Triple-A New Orleans (Pacific Coast League League) before the game. . The Mets play in St. Louis on Monday, when RHP Collin McHugh (0-0) faces Cardinals RHP Joe Kelly (4-6, 3.61). . The Marlins will send RHP Ricky Nolasco (10-12, 4.78) to face Milwaukee RHP Mike Fiers (8-6, 2.85) on Labour Day.