Jimenez (10-12) allowed three runs and five hits, struck out six, hit two batters and walked one in six-plus innings. It was a big improvement from his last start, when he walked five and gave up six runs in 3 2/3 innings against San Diego on Aug. 30.
After that performance, Iannetta talked to Jimenez about using his 97-mph fastball more. Jimenez acknowledged he relied on his breaking ball too much against the Padres.
"Obviously he heard what I had to say and he processed it," Iannetta said.
The first 16 pitches Jimenez threw against Houston were fastballs, and he gave up just one hit through the first four innings.
"I'm really happy, especially after having such a bad game my last start," Jimenez said.
After Jimenez left in the seventh, three relievers shut the door on Houston. Brian Fuentes pitched the ninth to earn his 27th save in 31 chances.
The Rockies, who closed to five games behind Arizona in the NL West, have won three of their first four on the current six-game homestand.
"We're right there," Barmes said. "Nobody in here's given up yet."
The Astros fell to seven games behind Milwaukee, who beat San Diego 3-2 on Friday, in the NL Wild Card race.
"We are at a point where we have to win every game," Astros manager Cecil Cooper said. "We have to come to the park with that in mind."
Brian Moehler (10-6) gave up five runs and six hits, walked three and struck out four for the Astros, who had won 10 of their last 12.
The Astros had an off day Thursday off after sweeping a three-game series against the Chicago Cubs in Wrigley Field.
"Sometimes when you're playing well and you have a day off, makes it a little difficult to bounce back," Cooper said. "We had a lot of momentum and all of a sudden you get a day off and you cool off a little bit."
The Rockies broke a scoreless tie in the fourth. Willy Taveras reached on an infield single, Matt Holliday was hit by a pitch and Brad Hawpe singled up the middle to score Taveras. Garrett Atkins drove in Holliday with a sacrifice fly, and after Ian Stewart flew out, Troy Tulowitzki singled home Hawpe to make it 3-0.
"The most frustrating point of the game for me was the fourth," Moehler said. "I didn't make bad pitches, but they found holes with the hits they got in the inning."
The Rockies chased Moehler in the fifth. Barmes led off with his eighth home run of the year, and two outs later Colorado loaded the bases on two walks and a single by Atkins. Fernando Nieve relieved Moehler and walked Iannetta on four pitches to give the Rockies a 5-0 lead.
Houston got a run back in the sixth on an RBI single by Geoff Blum.
"We had a chance to get back in the game late and could have used a big base hit from a couple of different spots and didn't get it," Cooper said.
Rockies manager Clint Hurdle said he was happy Jimenez bounced back from his previous start.
"He was coming after people, and he started mixing in some other pitches," Hurdle said. "It was an effective outing for him."
Eric Young, a member of the Rockies during their inaugural season in 1993, will officially retire as a member of the Rockies. The club will honor him with Eric Young day on Sept. 12. ... The Astros staff had a 1.85 ERA during their eight-game winning streak.