Ramirez tagged a solo shot in the second inning and finished 3-for-4 with two RBI. Colvin's two-run blast in the seventh gave the Cubs a 6-2 lead and provided the momentum the Cubs needed to post only their second win in seven games.
Ryan Dempster (4-5) notched the win, going 6 1/3 innings, surrendering three runs on six hits while walking two and striking out seven. Carlos Marmol was summoned to get the final two outs for his 12th save after the Astros scored two in the ninth.
Roy Oswalt (3-8) was saddled with the loss, getting roughed up for six runs on nine hits over seven innings of work.
Jeff Keppinger and Humberto Quintero socked homers for Houston.