ST. PETERSBURG, Fla. -- After the Boston Red Sox dropped two of three games to the Tampa Bay Rays this weekend at Tropicana Field, the notion of whether their postseason chances are still intact was on the mind of many.

But not the Red Sox players.

The Rays posted a 5-3 victory here Sunday night to take the series and leave Boston 6 ½ games behind Tampa and New York with 31 games remaining in the regular season. These teams face each other three more times in September at Fenway Park, and the Sox also have six games remaining against the Yankees, who share the AL East lead with the Rays.

“It’s not over yet,” said Red Sox catcher Victor Martinez. “We’ll keep playing hard and see what happens.”

Following Sunday’s loss, the Red Sox packed their bags and traveled to Baltimore, where they’ll face the Orioles in a three-game set, beginning Tuesday at Camden Yards.

Red Sox starter John Lackey worked 6 1/3 innings against the Rays and allowed five runs on nine hits with three walks and seven strikeouts. The right-hander surrendered a pair of home runs, to Carlos Pena (solo shot in the fourth) and Carl Crawford (two-run blast in the sixth with Boston ahead 3-1).

“[Lackey] did a lot of good things, but when he made the mistakes he really paid for them,” said Red Sox manager Terry Francona.

Lackey cruised through the first five innings, but Tampa touched him for three runs in the sixth and added another in the seventh.

“I’m still trying to figure it out,” Lackey said. “I felt way too good to give up five runs.”

Lackey said after the game that he thought it was the best he’s thrown the ball in years.

“Tonight I had as good of stuff as I’ve had in a long time,” he said.

But he only has a loss to show for it, dropping his record to 12-8.

“He threw the ball well,” said Martinez. “Crawford and Pena got two pitches that we were trying to go away, but [the pitches] came back over the middle and they both put a good swing on it.”

Despite the loss and the missed opportunities this weekend, Lackey believes the Sox can remain in contention over the final five weeks of the season.

“I’m not a math whiz, but I think it’s doable,” Lackey said.

Big game, James: Rays starter James Shields earned the victory to become the club’s all-time leader in wins (56) and games started (145), surpassing Scott Kazmir in both categories.

“It means a lot,” Shields said. “This organization has given me the opportunity to be able to pitch as long as I have here and hopefully I get a ton more. It definitely means a lot, but my focus right now is to go to the playoffs and win a World Series.”

The right-hander worked 6 2/3 innings Sunday and allowed three runs on seven hits with one walk and eight strikeouts.

CC's in fine company: Crawford’s homer in the sixth inning was the 100th of his career, allowing the Rays left fielder to become the eighth player since 1900 to reach 100 homers, 100 triples and 400 stolen bases. He joins Ty Cobb, Tris Speaker, Lou Brock, Frankie Frisch, Kenny Lofton, Paul Molitor and Tim Raines.

“Feels good,” Crawford said of his achievement. “I’m proud to be in elite company. It makes me want to see how far I can go.”

Crawford finished the night 2-for-4 and now has a career .467 average against Lackey.

Stopped cold: Martinez is not afraid to block the plate and he showed that again on Sunday when Pena attempted to score from second on a base hit to center field. Red Sox outfielder Darnell McDonald made a strong throw home, where Martinez was waiting for the one-hopper as Pena slid in and spiked Boston’s catcher. Pena was out and Martinez was in pain. After a few minutes, he was able to shake it off and remained in the game. He said everything was fine afterward.

May I assist you? McDonald now has eight outfield assists this season. He notched his seventh as a center fielder in gunning down Pena and becomes the first Red Sox center fielder to reach that mark since Coco Crisp in 2007.

A first for Navarro: Red Sox rookie infielder Yamaico Navarro recorded his first career RBI, a tying single in the fifth inning off Shields. “We played him because we thought he could help us win,” Francona said.