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HOUSTON -- Brooks Conrad filled in ably for an injured Chipper Jones on Tuesday night.

Now the Atlanta Braves have to wait and see how long he'll be their third baseman.

Conrad's two-run homer in the ninth inning powered the Braves to a 4-2 win over the Houston Astros.

The Braves were trailing 2-1 after the Astros scored a pair of runs in the eighth inning off Atlanta errors before Conrad's shot to right field off Houston closer Matt Lindstrom (2-3).

Alex Gonzalez singled to set up Conrad's go-ahead shot. Conrad entered the game in the bottom of the sixth inning to replace Jones, who injured his left knee.

"It was really big," Conrad said of the comeback. "He goes down like that and it was tough, but we pulled through and won the game and it was really huge."

Jones said after the game that he didn't think the injury was to his anterior cruciate ligament but that he heard a pop and had significant pain in his knee. He'll wait until Thursday to get an MRI in Atlanta.

Troy Glaus added a solo homer off Lindstrom in the ninth and also drove in Atlanta's first run in the seventh inning.

"I am just devastated," Lindstrom said. "J.A. pitched a great game. The guys battled back, so it is really hard to swallow right now. I don't know what else to say other than I take responsibility and I look forward to getting back out there and working on my mechanics and getting my location back."

Jonny Venters (4-0) got the win after striking out Jason Michaels to end the eighth inning and Billy Wagner pitched a perfect ninth for his 28th save.

Atlanta's big ninth inning allowed the team to overcome another sloppy defensive night. The Braves committed three errors for the second straight game.

Michael Bourn tripled in the eighth inning and tied it on an error by Gonzalez on a bad throw home to Brian McCann on a ball hit by Jeff Keppinger. Keppinger reached first on a fielder's choice. Braves starter Jair Jurrjens then intentionally walked Hunter Pence and was replaced by Peter Moylan.

Houston went ahead on an error by Omar Infante when he missed the catch at second, allowing Keppinger to score.

"Just a great win," Braves manager Bobby Cox said. "The way J.J. pitched and then Chipper gets hurt, to ... win the game, adversity staring us right in the face and we came back."

Glaus put Atlanta up 1-0 with an RBI-single in the seventh inning. Astros starter J.A. Happ set up that score by walking Conrad to start the seventh before walking McCann with one out.

Jurrjens allowed six hits and two runs in 7 1/3 innings.

Happ did not factor in the decision, but was much better on Tuesday than in his last start where he allowed seven earned runs in one-plus innings. He yielded just two hits and a run in 6 1/3 innings in his third start for the Astros since being traded from the Philadelphia Phillies for Roy Oswalt.

"Tonight I was better at mixing things up and throwing more strikes," Happ said. "I was around the plate and still kept the ball where it needed to be a lot more often tonight."

Rick Ankiel robbed Carlos Lee of a hit with one out in the fourth inning with a nifty diving grab on his fly ball to center. Ankiel dove headfirst to snag the ball and bounced awkwardly on the grass as he landed with his glove between his legs but with the ball sitting firmly in it.

Chris Johnson singled after that but Jurrjens struck out Brett Wallace to end that inning.

Jason Castro singled in the fifth inning before Happ reached on an error by Jones. But Jurrjens retired the next three Astros to end the inning.

Happ retired the first seven batters he faced before walking Ankiel with one out in the third inning. But he got out of that inning unscathed after striking out Jurrjens before Ankiel was picked off trying to steal second base.

He didn't allow a hit until a double by Jones with two outs in the fourth inning. Happ intentionally walked Matt Diaz before McCann popped out for the third out.

He sailed through the next two innings, facing the minimum in the fifth and sixth, before the walk to Conrad to start the seventh. The run-scoring single to Glaus chased Happ.

He was replaced by Wilton Lopez, and the Astros turned a double play to limit the damage.

Jones was injured fielding a ball in the sixth inning. He grabbed a grounder hit by Pence and jumped in the air as he made the throw to first base to get Pence out. He then fell to the ground where he remained for several minutes while trainers and coaches crowded around him. He was helped to his feet and walked gingerly off on his own power.

Game notes

Right fielder Jason Heyward was scratched from Atlanta's lineup because of a sore right knee. ... The Astros gave Cox a cowboy hat and a pair of boots to honor his career before the game. Houston manager Brad Mills and hitting coach Jeff Bagwell handed him the gifts. ... Cox chatted with Orlando Magic coach Stan Van Gundy and his brother, former Houston Rockets and New York Knicks coach Jeff Van Gundy, in the dugout before batting practice on Tuesday.