DETROIT -- Carlos Pena kept up his torrid hitting and helped Nate Robertson feel good again at home.
The win, the Tigers' fifth straight victory and eighth in nine games, was Robertson's first since July 20.
The Tigers matched their longest winning streak of the season and improved to 6-1 on their nine-game homestand. The A's, beginning a 10-game road trip, have lost seven of their last eight and fell into third place in the AL wild-card race, one game behind New York and Cleveland.
"It was the Robertson and Pena show tonight," Detroit manager Alan Trammell said.
Pena gave the Tigers a 1-0 lead in the fourth with a homer into the bleachers in right-center. Ivan Rodriguez and Magglio Ordonez singled with one out in the sixth and Pena then drove Dan Haren's 2-2 pitch into the stands in right for his eighth of the season.
"I'm frustrated that he beat me," Haren said. "Just because he's been the guy on fire. He's hot right now."
Pena, who also doubled, is 7-for-13 (.539) with five homers and 10 RBI since being recalled from Triple-A Toledo on Aug. 24. He spent most of the summer in the minors after hitting .181 with the Tigers to start the season.
"He's locked in," Robertson said. "He comes off the field and there's no emotion on his face. It's like he's ready to go out and do it again."
Pena's second homer sailed high into the twilight and Oakland right fielder Nick Swisher appeared to have tracked it down near the wall. It stayed up, however, and dropped five rows into the stands.
"It looked like he lost it in the twilight," Trammell said, who added that Pena's recent hot streak almost certainly means he'll be back in the lineup Wednesday. He started as the designated hitter Tuesday in place of Dmitri Young, who left Sunday's win over Toronto after fouling a ball off his left toe.
"Somehow, some way we'll have to get him into the lineup tomorrow," Trammell said.
Robertson (6-10) gave up one run and two hits in eight innings. He struck out six and walked two in winning for the first time in six starts.
Fernando Rodney pitched the ninth for his sixth save.
Haren (10-10) gave up 10 hits and struck out six in 7 1/3 innings. He was pulled for Ricardo Rincon as Pena came to the plate for the fourth time. Rincon struck him out.
Oakland's Bobby Crosby doubled to lead off the seventh and scored on Dan Johnson's sacrifice fly.
The A's swept a three-game series from Detroit on July 29-31 when they were the hottest team in baseball, but the roles seemed to reverse when the teams met Tuesday.
"I thought we pitched well enough to beat them but just didn't hit," Oakland manager Ken Macha said. "The major concern is that if you have one, two or three guys struggling, that would be fine; but we've got about seven or eight struggling right now.
"That's a major concern."
Haren's streak of 22 innings without allowing a homer ended with Pena's shot in the fourth. ... Detroit 3B Brandon Inge's fielding error in the fifth was his team-high 19th of the season. ... Tuesday was the Tigers' fourth straight game with at least 10 hits. ... Oakland INF Eric Chavez missed the game to be with his wife, Alex, who gave birth to the couple's first child. He is scheduled to return Wednesday.