One day after being traded for Manny Ramirez, Bay filled the disgruntled slugger's role in left field and with clutch hitting by tripling in the 12th inning then scoring on Jed Lowrie's single that gave Boston a 2-1 win over the Oakland Athletics.
"It definitely ranks up there with one of the better moments I've had," Bay said.
Bay was obtained from Pittsburgh in the deal that sent Ramirez to the Los Angeles Dodgers after he had criticized the club in recent weeks and missed two games with what he said was a sore knee although MRIs showed no problem.
"He's an unbelievable player," Boston starter Tim Wakefield said, "and for him to score the winning run, it's great stuff."
Bay scored both of Boston's runs, reached base four times and made two run-saving catches near the left-field line.
He didn't put the ball in play in his five at-bats -- two walks, a hit by pitch and two strikeouts -- before he came up with two outs in the 12th against Alan Embree (1-4).
He hit the ball high to left field with the crowd hoping for a homer. His teammates thought it was.
"We all did," said Lowrie, who drove in both runs. "We jumped up on the top step."
But the ball grazed the wall and Bay slid into third.
"I'm lucky it stayed in the park because it was a bad pitch," Embree said. "I tried to throw the breaking ball down and it stayed up."
Embree walked J.D. Drew intentionally and Lowrie, who had left the bases loaded in the 10th, hit a tapper past the mound. It was too high for Embree, and shortstop Bobby Crosby charged and threw the ball to first. But Lowrie beat the throw and Bay scored.
"It was just perfectly placed," Oakland manager Bob Geren said. "Maybe that's a typical finish for such a well-pitched game."
"Having met these guys eight hours ago, everybody's been extremely positive," Bay said. "You jump around with those guys, I felt like I'd been here all year. We were like little kids."
Mike Timlin (4-3) got the win. He was the last of five Boston relievers who allowed one run in 5 2/3 innings. It was just the second win in seven games for second-place Boston, which remained three games behind Tampa Bay in the AL East.
Oakland is 2-13 in its last 15 games.
Brad Ziegler shut the Red Sox out in the eighth and ninth, extending his record streak to start a career to 32 scoreless innings.
Bay, batting fifth, received standing ovations when his name was announced with the lineups before the game and again when he came up for the first time.
"I didn't really know what to do," he said. "It was all new to me. It was very flattering."
Bay made two nice plays in the field. He ended the Oakland fifth with a sliding catch on Ryan Sweeney's sinking flyball near the left-field line with Crosby on third. With a runner at second with two outs in the ninth, he got a good jump on Daric Barton's soft liner to left and backhanded it.
Boston scored in the second against Justin Duchscherer when Bay walked, went to third on Drew's double and came home on Lowrie's sacrifice fly.
The Red Sox obtained Bay just before Thursday's deadline for non-waiver trades, hoping to change the clubhouse mood from turbulence to tranquility. Francona held a rare team meeting before the game against Oakland.
In one game Ramirez missed after complaining about a sore knee, the Red Sox lost 1-0 to the New York Yankees and Joba Chamberlain on July 25.
"You expect to see him after David" in the lineup, Embree said. "It sounds like it was time for a change of scenery for both sides. Hopefully both sides end up walking away from this and going, `OK, I can live with it."'
For one game, at least, the Red Sox certainly could.
- Red Sox 3B Mike Lowell strained his right hip beating out his single in the 10th and Francona said he would be checked Saturday.
- The Red Sox recalled RHP Chris Smith from Triple-A Pawtucket to take the roster spot of RHP Craig Hansen, who was traded to Pittsburgh.
- The Red Sox reached the 2 million mark in attendance at the earliest point in club history, their 54th home game. The crowd of 37,832 increased the total for the season to 2,032,637. The previous record of 56 games was set in 2006 and matched in 2007.