By Maggie Cassidy
Globe Correspondent

Before last night’s game, a frenzy surrounding Manny Ramirez’s departure to the Dodgers and Jason Bay’s arrival from the Pirates had taken over Fenway Park.

But while Bay shined in his Red Sox debut, reaching base three times, scoring both Boston runs, and tripling to start the winning rally in the 12th inning, another star emerged. One who’s been with the Sox for almost a month.

Jed Lowrie, who was recalled from Pawtucket July 13 after Julio Lugo was placed on the 15-day disabled list, drove in Bay twice – including the deciding run on an infield single – to help lead the Sox to a 2-1 win over the Oakland A’s.

“It was just a matter of me going out there and trusting my game,” Lowrie said. “I was able to get a couple hits and hit a sac fly and hit a sac bunt, so I felt like I did it all tonight.”

Lowrie did it all and more, even shifting from shortstop to third base after Mike Lowell left with a strained hip in the 10th inning. With two outs in the bottom of the 12th, Lowrie ended the game with a grounder up the middle that A’s shortstop couldn’t field cleanly. Lowrie beat Crosby’s throw to first base as Bay crossed the plate.

“It was exciting to have him out there,” Lowrie said of Bay. “He made a great debut, and I’m excited to see him play every day.”

Lowrie and Bay collaborated for Boston’s first run, in the second inning. After a sustained ovation from the Fenway crowd, Bay walked in his first plate appearance, and raced to third on J.D. Drew’s double to right. Lowrie followed with a sacrifice fly to deep left on an 0-1 count, easily scoring Bay.

After Bay was hit by a pitch leading off the bottom of the fourth, Lowrie moved him to third with a single to right, but Kevin Cash grounded into a double play to kill the scoring chance.

Lowrie nearly ended the game in the 10th. Lowell started a two-out rally with an infield single (he was injured on the play while running to first) and Bay and Drew followed with walks. Lowrie worked the count full against A’s closer Huston Street before lining out to center.

No worries for Bay, though, who set up Lowrie’s winning hit in the 12th with a triple high off the wall in left-center.

“It’s been a great day,” Bay said. “It would have been nice for us to do it in nine innings, but to be a part of it in a way I was, it was a pretty good day.”

Oakland manager Bob Geren would have liked to see it end otherwise.

“[Lowrie] was coming in full speed and it was a close play at first. It was a tough play,” he said. “You’ve got to come in. It was perfectly placed.

“You hate to see a game end on a little hit like that, but then again, maybe that’s probably typical as well as the ball was thrown tonight by both teams. Maybe that’s a typical finish for such a well-pitched game by everybody involved.”

Like Bay, Lowrie said he and the rest of his teammates are still absorbing all the changes, but expect good things in the future.

“We just decided that we were going to move on today, start new,” Lowrie said. “We’re going to look back at the end of the season at today, and decide whether we did it from today, and if we did, we make it to the playoffs, if not, we gave it our best.”