The Braves were trailing 1-0 and down to their final strike in the ninth when McCann drove a 1-2 pitch the opposite way, the ball just clearing the wall in left-center.
The All-Star catcher stayed in the game behind the plate and two innings later, he ended it with his fourth homer of the season - a towering drive down the right-field line, just inside the foul pole against Jeff Fulchino (0-2).
Cory Gearrin (1-1) escaped a bases-loaded, one-out jam in the top of the 11th, helped by a disputed call, and was rewarded with his first career win.
McCann was supposed to get the day off, but he wound up leading the Braves to their fourth straight win. Mark Melancon blew the save in the ninth, ruining a brilliant performance by Wandy Rodriguez. The Astros starter pitched five-hit ball over eight scoreless innings but the Astros' beleaguered bullpen couldn't hold it.
Brett Wallace broke up a scoreless duel between Rodriguez and Derek Lowe with a seventh-inning homer.
The Braves didn't do much offensively, even with the return of Chipper Jones and Jason Heyward to the lineup. Jones, who had missed the last two games with a slight meniscus tear in his right knee, moved well at third base but struck out twice in the late innings with runners aboard.
Heyward started for the first time in seven games after undergoing an MRI exam on his right shoulder.
The Astros squandered a chance to go ahead in the 11th against Gearrin. Brian Bogusevic, who entered as a defensive replacement in the eighth, reached on a bunt single and stole second. Wallace was walked intentionally, and it looked as though the Astros had loaded the bases when Matt Downs was hit on the left elbow.
But plate umpire Alfonso Marquez ruled immediately that Downs raised his elbow to let the ball strike him. After a brief argument, Downs returned to the box and struck out. Clint Barmes walked to fill the bases, only to have J.R. Towles hit a hard grounder right at shortstop Alex Gonzalez, who started the 6-4-3 double play.
Rodriguez had his sixth straight start of at least seven innings, allowing only two runners to get as far as second base. But the Astros' bullpen, which came in with an ERA above 5.00, faltered again. Houston has converted only five of 16 save chances.
Lowe was breezing along until the seventh, when Wallace drove a 3-1 pitch about four rows deep in the left-center seats to put the Astros ahead. The Braves starter went seven innings, allowing five hits, no walks and striking out four.
Melancon benefited from two stellar defensive plays to start the ninth. Downs made a diving stop at third on Dan Uggla's hard-hit grounder, hopping up in time to make the throw to first. Then Eric Hinske drove one to the wall in right, but Hunter Pence made the catch crashing into the padding.
Finally, McCann hit it where no one could make the catch. Melancon left a breaking pitch hanging over the plate, and McCann sent it out the opposite way.
-- NOTES: The Braves said RHP Peter Moylan underwent successful surgery for a bulging disc in his lower back. He's expected to be out two to three months. ... The Braves went 5-3 on their homestand and now begin a seven-game road trip that stretches from coast to coast. They start out in Arizona on Wednesday, visit Los Angeles on the weekend for an interleague series against the Angels, then travel back to the East Coast for a two-game series at Pittsburgh. ... Rodriguez came into game 2-2 with a 4.21 ERA in nine career appearances against the Braves. He had his longest career outing vs. Atlanta, having gone seven innings in three previous starts.
Atlanta Braves' Brian McCann follows his walk off two-run home run in the eleventh inning of a baseball game against the Houston Astros Tuesday, May 17, 2011 in Atlanta. Atlanta won 3-1. / photo: Associated Press
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