Manager Tony DeFrancesco said the team needed another right-handed hitter on the bench with outfielders Justin Maxwell and Ben Francisco questionable to play with minor injuries. The Astros only had left-handed bats off the bench Wednesday.
"We feel like we have a little more breathing room," general manager Jeff Luhnow said.
DeFrancesco wants to give Dominguez, 23, a chance to show his abilities over the final month of the season.
"We really like his defense," DeFrancesco said. "He's a young kid who's hopefully going to be able to play at this level and make the adjustments."
Dominguez, acquired in the deal that sent Carlos Lee to the Marlins, played in four games with the Astros in early July. At Oklahoma City, Dominguez batted .298 with two homers and 23 RBIs in 45 games. He was batting .368 in his last 10 games.
"He does show some power, but we're waiting for him to have some more consistency," DeFrancesco said. "A third baseman in this league is a guy that's going to have to drive the ball and hit for power and drive in runs. He had a great week down there, so we thought it was the time for him to get up here and see what he can do."
Dominguez said he wasn't expecting to get called up before September but he was excited to be back in Houston.
The Astros will need a starter for Monday's game in Pittsburgh with Keuchel set to pitch that day with Oklahoma City. Luhnow said right-hander Edgar Gonzalez, who gave up four hits over seven innings for Oklahoma City on Wednesday, is a leading candidate to start Monday. The Astros will probably look outside their own pitching staff.
"We've talked about possibly going to a six-man rotation and Edgar is a candidate for that," Luhnow said. "We might get a chance to get him up here and see him on Monday. We still have a few days to figure that out."
Gonzalez signed with the Astros on Aug. 23. He started the season with Triple-A Colorado Springs, a Rockies affiliate, before making six starts with Monterrey in the Mexican League. On the season, he is 6-5 with a 3.84 ERA.