CHICAGO -- Brett Wallace started at third base on Tuesday for the fourth time in the past six games, with Scott Moore getting the nod at first. Moore had been starting at third with Wallace at first earlier in the month, but manager Brad Mills wants to give Wallace a long look at the hot corner.

Wallace was drafted as a third baseman before being moved to first base, which is where he played for the Astros last season. He took up third again this spring but has limited experience at the position at the Major League level.

"Wally played a little bit there this spring and looked pretty good, so we just kind of want to give him some time down there and see how he does, see if that's an option for us," Mills said.

Mills also didn't rule out Wallace seeing some time at shortstop, where he appeared in 10 games at Triple-A Oklahoma City this season before being called up. He has never appeared at shortstop in the Majors.

"We want to answer as many questions as we can, that being one of them," Mills said.

Barnes basks in glow of first Major League homer

CHICAGO -- Prior to Tuesday's game, bench coach Joe Pettini offered congratulations to outfielder Brandon Barnes on hitting his first career homer on Monday night at Wrigley Field. He then jokingly reminded Barnes to enjoy the moment.

"I hit my first one here," Pettini told Barnes, "and then I didn't hit another one."

Sure enough, Pettini slugged his only Major League home run in July 23, 1980, for the Giants, off Guillermo Hernandez. Barnes, who began the year in Double-A and was called up last week from Triple-A, homered off Jeff Samardzija.

Barnes received about 30 text messages, 10 voicemails, and countless messages on Facebook and Twitter from friends and family after the game, congratulating him for the homer. Barnes said that hitting the homer at Wrigley has extra significance.

"There's such great history here, and it's exciting to get in there and have a productive at-bat," Barnes said.

Barnes hit 12 homers in 399 career Minor League at-bats, so he's likely to hit more in the bigs if he gets a good pitch to hit. Pettini, meanwhile, had 344 career at-bats in the Majors from 1980 to 1983 and finished with one career homer and 20 RBIs.

Altuve refining his running game

CHICAGO -- All-Star second baseman Jose Altuve entered play Tuesday as one of just four players in the National League with at least 35 extra-base hits and 25 stolen bases, joining Jose Reyes, Michael Bourn and Shane Victorino.

Altuve stole just seven bases in 221 at-bats in his debut season in 2011 and has been refining his running game with experience. He's also worked on getting better jumps and reads with first-base coach Bobby Meacham.

"The season has moved along, and he's really found out when to run, when not to run and who he can run against," manager Brad Mills said. "He's progressed with that very nicely, and he's been able to pick what pitchers and what times to run, which is big."

Altuve stole a base in four consecutive games last Sunday through Wednesday, becoming the first Astros player to do that since Bourn in 2011 and the first Houston second baseman since Craig Biggio in 1994. Altuve ranks 10th in the NL and first among NL second basemen with 25 steals.