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MIAMI (AP) -- Matt Treanor found a perfect time to deliver his first major league RBI.

Treanor singled home the winning run over the outstretched glove of second baseman Willie Harris with two outs in the 11th inning, giving the Florida Marlins a 2-1 victory over the Chicago White Sox on Thursday night.

"I told myself to put the ball in play," Treanor said. "I got enough to hit it over him."

The victory helped overcome the Marlins' possible loss of pitcher Josh Beckett to another injury. The World Series MVP left his start in the fourth with a strained muscle on the side of his back. He just returned from a 15-day stint on the disabled list because of a blister on his right middle finger.

"I felt something go pop, and I thought I could get through it," Beckett said. "As it turns out, it was a muscle."

The hard-throwing right-hander is day to day.

Luis Castillo led off the 11th with a walk, stole second and went to third on Mike Lowell's flyout to center.

Treanor hit a 2-2 pitch from Cliff Politte (0-2) for his first RBI. Before Treanor's winning hit, White Sox relievers held the Marlins hitless in 2 2-3 innings.

"I had a feeling he was going to stay away from the plate again," said Treanor, who missed on an outside pitch before his hit. "I told myself to just put the ball in play."

Beckett's departure ended his short duel with Chicago ace Esteban Loaiza, who allowed only one run and five hits in eight innings.

Armando Benitez (2-0) pitched two scoreless innings for the win.

After the game, the Marlins acquired Billy Koch and cash from the White Sox in exchange for minor-league infielder Wilson Valdez.

"He will be a good fit for them," White Sox manager Ozzie Guillen said of his former closer, who struggled in 1{ seasons in Chicago.

Beckett had an 0-2 count on Jose Valentin with two outs in the fourth when he stepped off the rubber. Pitching coach Wayne Rosenthal and assistant trainer Mike Kozak immediately came out of the dugout to tend to Beckett.

"The best thing about tonight is that I didn't get a blister," Beckett said. "I got this instead, though. It hurts to laugh."

After a brief conversation with his pitcher, Rosenthal motioned to manager Jack McKeon, who replaced Beckett with Ben Howard. He struck out Valentin to end the inning.

"He wanted to stay out there, but I made the decision to do what's best," McKeon said. "It's like I told him, we don't need any heroes out there at this point."

Beckett showed no ill effects from the blister, striking out eight of the first nine he retired. He allowed two hits and walked none.

The White Sox took advantage of Beckett's departure when Timo Perez singled in Miguel Olivo for a 1-0 lead in the fifth.

But the Marlins tied it in the bottom half on Alex Gonzalez's homer. Florida pitcher Dontrelle Willis, who pinch-hit for Howard, followed with a triple to the gap in right-center. But Willis was stranded as Juan Pierre struck out and Castillo grounded out.

"We played very good ball here," Loaiza said. "All games were very close. I pitched to win just like every other outing, but we just lost."

Game notes

The White Sox are 15-5 in the final game of a series. ... Chicago's Frank Thomas reached safely in his 24th consecutive game when he was hit by a pitch in the eighth. ... Willis got his second pinch hit of the season. ... The Marlins have homered in nine consecutive games. ... The first pitch Marlins reliever Josias Manzanillo threw was the 5,000th of his major league career.