BALTIMORE -- With infielder Jose Lopez called up prior to Thursday's game, White Sox manager Robin Ventura has additional flexibility to give players time off, including third baseman Kevin Youkilis, who was out of the starting lineup against the Orioles.

Ventura said the roster move gave him the opportunity to give Youkilis a rest for the day game following a night game and with the team traveling to Detroit for a key weekend series against the Tigers. Lopez started Thursday at third base.

"It's a day game and Youk's knee has kind of been barking the last couple of days," Ventura said. "Just clean it up and have him ready for [Friday]."

Catcher A.J. Pierzynski returned to the starting lineup Thursday after sitting out Wednesday's game. He is hitless in his last 14 at-bats and is 5-for-32 (.156) over his past 10 games.

Lopez called up, Flowers placed on paternity leave

SEA@CWS: Flowers drills go-ahead homer to dead center

BALTIMORE -- The White Sox had a busy morning before their matinee on Thursday in Baltimore, making five roster moves.

The team purchased the contract of infielder Jose Lopez from Triple-A Charlotte, where Lopez had been since the White Sox signed him to a Minor League deal on Aug. 15. Lopez hit .306 with 10 RBIs with the Knights.

Lopez, a career .262 hitter with the Mariners, Rockies, Marlins and Indians, was inserted into the starting lineup on Thursday, playing third base.

"This adds an extra infielder in case we have to move some guys around," Chicago manager Robin Ventura said. "He's a big plus for us. We've been going with quite a few pitchers, and really only three guys on the bench, so this is one of those that gets us to a better spot."

Catcher Tyler Flowers, who started Wednesday's game behind the plate, was placed on paternity leave, as his wife expects their first child. The White Sox purchased the contract of Hector Gimenez from Charlotte to fill Flowers' spot on the roster.

"I'm excited to be here and I'm ready to help win," said Gimenez, who was removed in the fifth inning of the Knights' game Wednesday when word came down of the callup. "That's the mindset I need to have here."

In addition, the White Sox gave pitcher Gregory Infante his unconditional release. Infante was 21-24 with a 3.79 ERA in 180 Minor League appearances. He pitched in five games for the White Sox in 2010, throwing 4 2/3 scoreless innings.

The White Sox also transferred pitcher Brian Bruney (left hip surgery) to the 60-day disabled list.

White Sox ready for critical series vs. Tigers

BALTIMORE -- Friday marks the start of a critical series for the White Sox, as they travel to Detroit to take on the Tigers, who entered play on Thursday three games behind Chicago in the American League Central race.

The White Sox are 4-7 against Detroit this season and have lost four straight, including a three-game sweep during the teams' last meeting July 20-22.

Shortly after that series, however, Chicago climbed into first place and has not looked back, giving the White Sox confidence heading into the Motor City.

"We've got to have a good weekend," White Sox second baseman Gordon Beckham said. "We've been on the other side of the coin, where we had to win series against a first-place team to get back in the hunt, and it's not easy. Every game lost to a team that's in the lead can be frustrating, so if we can go in there and just win one, to be honest, it's a victory for us."

With another four meetings with the Tigers in Chicago still on the schedule, Beckham said the team isn't placing too much stock on this weekend.

"Obviously, it's a big series, but we don't want to put too much pressure on ourselves," he said. "We're doing fine. There's no need to make it bigger than it is. We've got seven games left with them, and you want to win at least three or four of those games."

Worth noting

• The White Sox hit one home run over the first three games of the Orioles series, but still led baseball with 44 homers in August entering Thursday's finale and remained tied for second in the Majors with 170 this season.

• Rookie Dylan Axelrod's one-run, three-hit performance in 7 1/3 innings on Wednesday night gave the White Sox 73 quality starts on the season, tied for first in the American League with Detroit, Oakland and Tampa Bay.