Geoff Blum, who was booed by the fans at Minute Maid Park the night before for a perceived lack of effort running the bases, went 3-for-4 and delivered his third walk-off hit of the season with a bases-loaded single off reliever Mike MacDougal with two outs in the ninth.
"It's a sigh of relief," Blum said of reaching .500. "We knew we could get there, but it's nice to get there. That's just the first step. We have to take advantage of the next two games going into the [All-Star] break and then hopefully come out of the break on a good note."
The Astros got contributions from every corner of the clubhouse. Carlos Lee homered and had three hits, Miguel Tejada sparked the game-winning rally in the ninth with a leadoff single and Jeff Keppinger drove in the tying run in the eighth with a sacrifice fly.
But this night belonged to Bourn, who went 2-for-5 with his first three-RBI game of the season. He stole his league-leading 29th base, but it was his defense that made the biggest impact against the Nationals.
"He has just stepped up big offensively and has been huge, and I don't know where we would be without him from an offensive standpoint," Cooper said. "He's in the middle of all the rallies, and his defense has been outstanding. He's played terrific."
Bourn threw out a runner at the plate in the fourth and gunned down the potential go-ahead run in the ninth with a strike to catcher Ivan Rodriguez, who caught the ball on a short hop and lunged at runner Willie Harris as he passed by.
"You know what's on the line," Bourn said. "The game was tied, and I was trying to close in on the ball and throw it as quickly as I could. To tell you the truth, Pudge helped me out. I short-hopped him and he picked it off the ground and made the tag, and that helped us out tremendously. We came in the bottom of the inning after that and took care of business."
Rodriguez's emphatic tag only added to the drama of the play.
"The second one was a good throw, but it was a little bit towards the left side by probably four feet," Rodriguez said. "When I caught it, I still saw Harris coming in, and what I did was just dive like I was diving into a swimming pool and was able to tag him in the leg."
Nationals manager Manny Acta was quick to laud Bourn.
"Michael Bourn played a tremendous center field today," he said. "He made two great throws. He saved the game for them the whole day."
Behind ace Roy Oswalt, Houston was cruising through six innings with a 4-1 lead. Oswalt gave up consecutive doubles to start the seventh and was pulled from the game with numbness in two fingers in his pitching hand after throwing a first-pitch ball to Josh Bard.
Oswalt, who suffered the injury on his at-bat in the sixth, allowed three runs and five hits in six-plus innings. Jeff Fulchino (3-3) picked up the win by throwing a scoreless ninth and didn't allow any damage despite giving up two hits.
The Nationals scored twice in the seventh off Oswalt to get within 4-3 and took a 5-4 lead on Cristian Guzman's two-run single off Chris Sampson later in the inning. But Houston tied the game at 5 in the eighth on Keppinger's bases-loaded sacrifice fly.
"It's probably the first day he hasn't started against a left-hander, and we saved him just for that opportunity," Cooper said. "I told Kepp he's going to be my guy off the bench and drive in a run against a left-hander, and he did."
Bourn struck out to end the eighth and wasn't involved in the game-winning rally, but his fingerprints were all over the Astros' 11th win in 16 games.
"I felt like it was a game we needed to have," Bourn said. "There are certain games during the season I feel you need to get, and today was a game we needed to have to get us to .500. Hopefully, we can push forward from here."