CHICAGO -- If the White Sox truly are to make a playoff push, games like Friday's are exactly the type they'll need to figure out how to win.

With the American League East's last-place Orioles in town and White Sox starter Gavin Floyd in command, Chicago still could not find a way to punch through with a victory. Instead, the White Sox offense proved listless and Floyd eventually unraveled in a 5-1 loss in the series opener at U.S. Cellular Field.

It was a humbling defeat for the White Sox, who fell to 3-4 this season against the Orioles and dropped 3 1/2 games behind the Tigers in the American League Central.

"This time of year, you want to do well, and you want to compete, and you want to win games," said White Sox designated hitter Jim Thome, "and that's the frustrating part."

Friday marked the beginning of a 20-game stretch in which the White Sox (62-60) will not encounter a single off-day. They will, however, encounter some of the American League's best in Boston, New York and Minnesota, all on the road -- making this particular series against the Orioles (50-72) even more crucial as the White Sox battle the Tigers for first place in the AL Central.

Floyd certainly did his part, cruising through seven innings before ultimately running out of steam in the eighth frame. He lasted 7 1/3 innings, allowing four runs on seven hits with seven strikeouts and two walks.

"Floyd pitched a tremendous game," Orioles manager Dave Trembley said. "He had very good movement. I didn't know he had such a good cutter. He was cutting the ball in on left-handed hitters. We finally broke through with some big hits."

Floyd (10-8) had allowed just four hits through seven innings, and he struck out Matt Wieters looking to begin the eighth before finding trouble. Felix Pie singled on a line drive to right field. And Brian Roberts followed by providing the big blow, a two-run home run, off the back wall of the right-field bullpen for a 3-1 Orioles lead. It was Roberts' second home run of the contest, his first coming on a solo shot in the third inning. Friday also marked his second career multi-homer game. He last accomplished the feat on Sept. 6, 2006, against the Angels.

"I think it's very disappointing when you do well that long and then one pitch changes the game," Floyd said.

Floyd had been arguably Chicago's best pitcher over the past three months. Before Friday, Floyd was 8-3 with a 2.46 ERA in 16 starts since May 22.

"Gavin Floyd has thrown the ball really well all year," Roberts said. "He threw the ball great tonight, but when you get pitches to hit, you have to do something with them. Sometimes, it works out. When you're going good, that seems to happen."

Floyd, who entered the eighth locked in a 1-1 tie, did not retire another hitter. He surrendered a double to Cesar Izturis and intentionally walked Adam Jones, ending his evening. He threw 115 pitches, 70 for strikes. After Izturis was thrown out trying to steal third, White Sox reliever Matt Thornton allowed Jones to score to close out Floyd's pitching line.

The defeat overshadowed another milestone for Thome. In the bottom of the fourth, he clobbered a 1-0 offering from Orioles starter Jeremy Guthrie 412 feet to dead center, his 23rd home run of the season and the 564th home run of his career, moving him past Reggie Jackson for 12th place on the all-time home run list. The shot proved to be the only offensive fireworks for the White Sox on a night that mostly consisted of missed opportunities, which began in the first inning.

With runners at first and second and nobody out in the bottom of the first, Guthrie picked off Scott Podsednik at second base. It was the first out of the inning, and Chicago did not produce a baserunner for the remainder of the inning.

White Sox manager Ozzie Guillen saw the play as a tone setter for the rest of the game.

"I don't know how that inning would have been turned around, but when that happened and you had the guy against the wall starting the game, you catch a big break," Guillen said. "After that, we couldn't recover. It's like a punch in the first round and you were fighting all the way back with that punch in your body, and you can't come back and recover from that one."

Chicago had its chances offensively again in the middle innings, but was unable to capitalize off Guthrie (8-12). With Jayson Nix at first base in the fifth, Podsednik perfectly executed a hit and run, driving a pitch through a vacant left side of the infield and moving Nix to third. But rookie Gordon Beckham followed by hitting into a double play to second to end the threat and the inning.

And in the sixth, the White Sox (62-60) again put two runners on base, this time with nobody out. Jermaine Dye lined a single to left field, and Thome followed with a walk. But Paul Konerko, Alex Rios and A.J. Pierzynski each flied out into the outfield to strand both runners.

As a result, Floyd was dealt just his third loss in his past 15 starts.

"With the lineup we have and the pitching we have, I think we should win every game," Floyd said. "But it's not the case. Nobody's perfect. You just kind of move on to tomorrow."