Lopez was signed to a minor league contract by Chicago on Aug. 14 after being designated for assignment by the Cleveland Indians. The 2006 AL All-Star is a .262 career hitter over nine seasons.
The 28-year-old was in the starting lineup at third base against the Orioles. He doubled in his first at-bat and made a fine catch of a line drive down the line in the bottom of the first inning.
"He's a big plus for us," White Sox manager Robin Ventura said. "We've been going with quite a few pitchers and we're only with three guys on the bench, so this is one of those (moves) that gets us to a better spot."
Flowers, meanwhile, is expecting the birth of his first child. To fill the void behind the plate, the White Sox purchased the contract of catcher Hector Gimenez from Charlotte. Gimenez hit .259 with Charlotte this season.
"He was good in spring training, so he's familiar with everybody," Ventura said. "That's part of the confidence of bringing him up here."
Chicago also transferred right-hander Brian Bruney to the 60-day disabled list and released minor league right-hander Gregory Infante, who spent more than seven seasons in the organization but appeared in only five games with the White Sox (in 2010). Bruney underwent season-ending surgery on Aug. 13 to repair the labrum in his left hip.