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8/17/2013 10:27 P.M. ET

Porter likes results from reformed outfield

ANAHEIM -- Astros manager Bo Porter has settled into an outfield configuration of Robbie Grossman in left, Brandon Barnes in center and L.J. Hoes in right, with Mark Krauss getting occasional starts in right. Chris Carter, who started in left to begin the year, has been limited to designated-hitting duties since his last appearance in the outfield July 25.

"It's good to have the flexibility on your roster knowing he can do it, but when he was playing the outfield early in the year, our roster construction was totally different," Porter said. "You look at the construction we have now, I like the fact we have three guys out there who have the capability of playing center field and have the range of a center fielder. You look at our pitching staff, and I think it has gotten better because overall the defense has been better."

Carter, who leads the team with 23 homers and 61 RBIs while hitting .213, has started 107 games, including 31 at first base, 36 in left field, 38 at designated hitter and two in right field.

"He'll DH and play more first base than he would with the current roster construction we have," Porter said. "If that roster construction was to change, it's good having the flexibility of knowing he can go play the outfield given a different situation. Just like [Brett] Wallace can play third base. You look at the way Matt Dominguez has played third base, and you don't want to move him from over there because he's playing such a good third base."

Triple-A season to influence September callups

ANAHEIM -- Astros general manager Jeff Luhnow and manager Bo Porter have begun talking about players who could be called up to the Major Leagues when rosters can be expanded to 40 on Sept. 1. There will be an initial handful of players coming up, but the majority of promotions won't happen until Triple-A Oklahoma City's season is over.

"We've started preliminary conversations about it," Porter said. "But with the Triple-A team fighting for a playoff spot, you want to be sensitive to the fact they actually have an opportunity to win that league. As their season winds down, we will get more in detail with the guys that will come from the first of September and who will leave there, that will come when the playoffs are over and still gives them the best opportunity to win the league."

Among the players we could see in Houston next month are outfielder Trevor Crowe, infielder Brandon Laird, outfielder/infielder Jimmy Paredes and pitchers Jose Cisnero, Paul Clemens, Rhiner Cruz and Jorge DeLeon -- all of whom have spent some time with the Astros this year. Outfielder J.D. Martinez, who's on a Minor League rehab assignment, will return if healthy.

Luhnow said Friday No. 3 prospect George Springer, an outfielder who leads the Minor Leagues with 34 home runs, would remain with the RedHawks until their season is over. He's currently not on the 40-man roster.

Luhnow was in Oklahoma City on Saturday and planned to talk to manager Tony DeFrancesco about possible callups.

"I think anybody who's been here already will get a first chance," he said. "We're going to have to figure out how to get reinforcements up here while at the same time not decimating the team there. They're having a good season, and we hope they finish strong and go deep in the playoffs. There's enough players to do that."

Fields, Lo to share closer's role for Astros

ANAHEIM -- For the first time since they traded closer Jose Veras to the Tigers on July 29, the Astros have narrowed the closing duties to rookies Josh Fields and Chia-Jen Lo. Manager Bo Porter had been employing a closer-by-committee approach until recently.

Fields picked up his second save of the season Wednesday at Oakland by tossing a scoreless 11th inning. Lo threw a scoreless ninth inning Friday to become the first Astros pitcher in 10 years to begin his career by making seven scoreless appearances.

"I'll fluctuate between Fields and Lo based on the workload previously leading up to that," Porter said. "It's a good option to have both of those guys pitching well."

Lo, who got his first save Tuesday in Oakland, was warming up to pitch the ninth inning of a two-run game Friday night before the Astros broke it open with a three-run homer by Chris Carter and a solo shot by Matt Dominguez. Still, Porter let Lo handle the ninth because he was warmed up.

"In that situation, you want to bring your closer in," he said. "Once you get the three-run homer, I made that decision. I'm not going to sit him back down and he's coming into the game."

Brian McTaggart is a reporter for MLB.com and writes an MLBlog, Tag's Lines. Follow @brianmctaggart on Twitter. This story was not subject to the approval of Major League Baseball or its clubs.