Mike Fontenot, Jeff Baker and Derrek Lee also homered for the Cubs, who have won eight of their last 11 games.
The Reds dropped their sixth straight road game despite starting pitcher Aaron Harang's first career home run. At 44-51, they are a season-worst seven games under .500.
In his first 11 games after missing nearly two months with a separated shoulder, Ramirez was batting .190 with one homer and two RBIs. But he followed Wednesday's two-hit, two-RBI game at Philadelphia with Friday's four-hit performance, looking like the former All-Star who has driven in 100-plus runs six times.
Ramirez's leadoff homer in the sixth put the Cubs ahead 4-3 and aided starter Randy Wells (6-4), who is 6-0 when receiving at least four runs of support. The rookie allowed seven hits in six innings.
Harang (5-11), who gave up nine hits and four runs in six innings, is 0-7 with a 5.17 ERA in his last 11 starts. After going 32-17 in the 2006 and 2007 seasons, Harang is 11-28 in 2008 and 2009.
