Chas McCormick homered for Houston, which split the two-game series with Colorado.
Bielak struck out four and walked three in 5 2/3 innings. Phil Maton, Rafael Montero, Ryne Stanek and Ryan Pressly then combined for 3 1/3 innings of one-hit relief.
Bielak’s scoreless outing was the longest by a Houston pitcher at Coors Field since Roy Oswalt threw a one-hit shutout on Sept. 6, 2008.
“Bielak was great today,” Astros manager Dusty Baker said. “He commanded the strike zone and I was surprised how good his breaking ball was in this altitude. He had quite a few swings and misses, couple balls hit hard to (shortstop) Jeremy (Peña) but fortunately for us they were hit right at him.”
C.J. Cron spoiled the shutout bid with a home run off Pressly in the ninth.
Bielak (5-5) joined the rotation when José Urquidy went on the injured list on May 1. The right-hander also tossed seven scoreless innings in a 4-1 victory against Colorado on July 4.
“I can only talk about my at-bats but not too much to hit,” Cron said of Bielak. “He threw me a couple good cutters away, that’s really all he threw out there. He didn’t throw very much off-speed so kind of just keeping us off balance with a pitch that we weren’t quite expecting.”
Colorado starter Austin Gomber (8-8) lost for the first time since June 19 at Cincinnati. He was charged with four runs and eight hits in six innings.
“Early he kind of had us off balance quite a bit with his changeup, his breaking ball and his fastball,” Baker said. “You’re always a little bit apprehensive and scared of this ballpark in a low-scoring game.”
Mauricio Dubón drove in Jake Meyers with a single in the second, and Kyle Tucker scored in the sixth when he doubled and came home on José Abreu’s single.
McCormick followed Abreu’s hit with his 12th homer of the season.
“It’s always nice to have a happy flight,” McCormick said. “It’s big to win today, we’ve got to carry that momentum into Oakland.”
THAT DIDN’T LAST
Colorado pitcher Fernando Abad got his first win in 2,226 days when the Rockies beat Houston on Tuesday night, but the celebration was short. Abad was designated for assignment before Wednesday’s game to make room for lefty Brent Suter to return from the injured list.
Astros: LHP Framber Valdez (calf) threw a bullpen session before the game and will start at Oakland on Friday night, Baker said. Valdez left Saturday’s start at the Los Angeles Angels in the seventh inning. ... LF Yordan Álvarez (right oblique discomfort) and Urquidy (right shoulder discomfort) were slated to make rehab appearances at Triple-A Sugar Land on Wednesday.
Rockies: OF Randal Grichuk (left groin tightness) was not in the lineup for the fourth straight game. He ran the bases Tuesday but with a day off Thursday he was given more time to recover.
Astros: RHP J.P. France (4-3, 3.31 ERA) will open a four-game series at the Oakland A’s on Thursday night.
Rockies: Have not announced a starter for Friday’s opener of a three-game series at the Miami Marlins.
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