Jason Giambi tries to keep the game simple see the ball, hit the ball.
Giambi was 8-of-11 (.727) with four RBIs in the series against the Devil Rays.
"He's hitting everything you throw to him," said Tampa Bay manager Larry Rothschild. "He doesn't get cheated in his at-bats. He's going to find a way to beat you and it doesn't matter what pitcher he hits against."
Gil Heredia (8-5) allowed six runs and 11 hits in 6 1-3 innings to win his fifth straight decision. The A's won their sixth straight at home.
"The key for me is to give myself a chance by throwing strikes," said Heredia. "I always think about just getting one more out and to keep going."
T.J. Mathews pitched the last 2 1-3 innings for his second save. Oakland traded its closer, Billy Taylor, to the New York Mets on Saturday.
Bobby Witt (6-7) allowed six runs four earned and five hits in three-plus innings for the Devil Rays, who have lost nine of their last 11.
"I didn't have good command, I couldn't keep the ball down and I was inconsistent," Witt said. "I never got untracked."
Tampa Bay's Wade Boggs went 2-for-4, tying San Diego's Tony Gwynn with 2,994 career hits. Gwynn had three hits Sunday against Houston.
Oakland snapped a 2-2 tie with six runs in the fourth inning, including Giambi's 22nd homer.
Miguel Tejada and Eric Chavez opened the fourth with solo home runs against Witt. After Witt walked two batters, he was replaced by Bryan Rekar, who then allowed the homer to Giambi and a solo shot to John Jaha, his team-leading 27th.
The four homers in an inning tied an Oakland record. The A's did it previously in the third inning on Aug. 21, 1997 against Boston, and Giambi was also involved.
Giambi has a season-best, nine-game hitting streak and is batting .472 (17-for-36) during that span.
"As long as he's going, we have a good chance," Chavez said. "He's the catalyst of the team. It's kind of contagious. We're all swinging the heck out of it and that's nice to see."
The A's took a 2-0 lead in the second. Witt threw Tejada's sacrifice attempt into the right-field bullpen, allowing Ben Grieve to score from first and Tejada to reach third. Mike Macfarlane followed with an RBI single.
Dave Martinez singled to score Terrell Lowery in the third, and the Devil Rays tied the game in the fourth when second baseman Randy Velarde committed an error on Aaron Ledesma's grounder, allowing Boggs to score from third.
Tampa Bay added four runs in the seventh, two on Tony Graffanino's home run. Terrell Lowery singled in a run and Ledesma scored on a wild pitch.
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