Chacin (10-10) rebounded from his shortest outing of the season with an effective effort. He was tagged for 11 hits and struck out just two but consistently pitched out of jams with the help of three double plays.
"They're aggressive hitters. I was able to throw my fastball for a strike and use my breaking ball and changeup when I had runners on base to get the out," Chacin said. "I'd prefer to give up a base hit than a walk."
The Astros had a hit in every inning but the seventh. They just couldn't come up with the big one when it counted. Twice they had runners on third base, but Chacin came up with the right pitch to get out of the inning.
"He surrendered 11 hits but because of walking only one guy and getting key outs he turns it into a good outing," Rockies manager Jim Tracy said.
Chacin also got some early offense to work with. All nine starters reached base for Colorado, which won its third straight. It's just the second time since June 18 the Rockies have won three in a row.
They needed all the offense against Houston righthander Brett Myers. Myers (3-13) came into Monday 7-0 with a 3.47 ERA in eight appearances against Colorado, seven of those as a starter.
The Rockies changed that with a big first inning. Eric Young Jr. led off with a walk, Dexter Fowler doubled and Gonzalez knocked both in with a double. One out later, Todd Helton singled to score Gonzalez, Ty Wigginton doubled and Helton scored on a groundout.
Chacin capped the inning with a two-run double over the pulled-in outfield that made it 6-0.
"We had a good scouting report on him," Gonzalez said of Myers. "His fastball is not the same, he's around 88, 90. The first pitch I saw was a curveball and I swung and missed. I thought he was going to come back with another breaking ball. I was expecting that pitch and I was able to drive it to right field and get two runs early."
Gonzalez made it 7-0 with a solo homer in the second, his 22nd of the year.
Myers gave up seven hits in the first 10 batters he faced but settled down. He went five innings and allowed seven runs on nine hits, struck out three and walked two.
"The ball was flat tonight. It didn't have any angle, it was straight," Myers said. "The ball was flat and they were just putting good swings on it. The ball didn't have any life on it. I was able to make the adjustment second inning."
Brian Bogusevic got the first big hit off Chacin, a homer to lead off the fourth to make it 7-1.
The Rockies added two more on Chris Nelson's two-run single in the eighth.
Matt Downs hit a pinch-hit, three-run homer off J.C. Romero in the ninth to make it 9-4. Houston loaded the bases with one out in the ninth before fill-in closer Rafael Betancourt got Jimmy Paredes on a sacrifice fly and struck out Clint Barmes for his third save.
"It was sure nice to see our guys battle back," Astros manager Brad Mills said. "Anytime you're down 9-1 going into the ninth inning and you make the other team bring in the guy they're using for their closer, there's some fight there."
Gonzalez has seven homers and 23 RBIs in 16 games since coming off the disabled list Aug. 6. ... Rockies relievers Huston Street (right triceps strain) and Matt Lindstrom (right arm nerve injury) were scheduled to throw one inning each for Triple A Colorado Springs in a rehab assignment Monday. ... The Astros activated OF Jordan Schafer from the 15-day DL. ... Houston right-hander Bud Norris will pitch Tuesday. Norris, who ranks ninth in the NL in strikeouts per 9.0 innings, has never faced the Rockies. Rookie Alex White will make his Colorado debut Tuesday. White was one of four players acquired from Cleveland in the trade that sent Ubaldo Jimenez to the Indians on July 31.