"That one was almost a must-win situation," Astros manager Cecil Cooper said. "I thought we really had to have that, and the guys really battled and hung in there with Z. I thought he had a chance to go nine the way he was going for a while there. All of a sudden in the seventh, we tied it up and were able to get him out of there. That was probably the key to the ballgame."
Blum drove in both of the Astros' runs, including an RBI groundout against Zambrano in the seventh that tied the game. In the ninth, he hit a soft liner on a 1-2 pitch from Guzman (2-1) into center field for Houston's third walk-off win of the year.
"Miggy's at third and he can run a little bit, so I know that I don't have to annihilate a ball to the warning track to get him to score," Blum said. "It's just got to be a medium-sized fly ball to get him in. Guzman is throwing 95-mph sinkers and 92-mph cutters, and fortunately with two strikes he left a ball out over the zone and I was fortunate enough to get on top of it and drive it to center field."
Astros starter Wandy Rodriguez, who had allowed 19 hits and 11 runs in 8 2/3 innings in his previous two starts, was terrific. He pitched seven innings and allowed five hits, including a homer in the second inning to Geovany Soto, and struck out six.
"He is the only reason we had an opportunity in the ninth," Blum said. "He went up against a formidable pitcher and we had to grind it out, and he's the reason we were able to get one run and tie it up and get the other run to win it, 2-1."
Chris Sampson (3-0) got the win in relief by throwing two scoreless innings. He has a 0.71 ERA in his last 10 appearances and hasn't allowed a run in his last six outings.
Rodriguez was told he was tipping his pitches in his previous start against Pittsburgh by catcher Ivan Rodriguez. Blum and teammate Darin Erstad also picked up on a pattern in the way Wandy Rodriguez moved his glove before certain pitches and alerted pitching coach Dewey Robinson.
"It's not my job or Darin's job to go straight to Wandy," Blum said. "I don't think he'd want to hear that from us. His relationship with Dewey is good enough to where we can tell Dewey and he can approach Wandy in the right manner and take care of things.
"It's a game of adjustments, and the reason Wandy was pitching so well was he was making adjustments quick. He had two bad outings and comes back and does this against a great hitting club like Chicago. It shows he's making the right adjustments."
Another key for Rodriguez was getting paired with catcher Humberto Quintero for the first time this season. Ivan Rodriguez had caught Wandy Rodriguez's first 12 starts, but Cooper opted for a change, and it appeared to pay off.
"The first couple innings he wasn't going after them," Quintero said. "He threw more aggressively in the last few innings. I told him before the game to go out and be aggressive and attack."
Zambrano held the Astros to leadoff singles in the first and second innings and had retired 17 of the 20 batters he had faced entering the seventh inning, retiring 14 in a row at one point. His eight innings of work are his most since he threw a no-hitter against the Astros last September in Milwaukee.
"We have a good enough offense to scratch out some runs, although in the early going I thought we were kind of going through [the motions] a little bit," Cooper said. "He had some real easy innings. He was in the sixth, I think, and hadn't thrown 60 pitches."
Hunter Pence led off seventh with a walk and raced to third when Carlos Lee (2-for-4) followed with a single. After Lance Berkman popped out, Pence scored on Blum's groundout to the right side of the infield to tie the game at 1.
"I was seriously just trying to make contact," Blum said. "You don't want to ground into a double play in that situation, but I needed to drive a ball to the outfield. I was fortunate to get a bat on one split-finger and get it in position where I didn't hit into a double play."