Wells (8-4) gave up a solo home run among six hits with two walks to win his fourth straight start. In his past nine starts he is 8-1.
Mike Fontenot hit a three-run homer and Derrek Lee drove in the other run for the Cubs, who have won four of their last six games.
The win puts Chicago in a virtual tie with St. Louis for the lead in the NL Central.
Alex Gonzalez hit a solo home run and an RBI double for the Reds, who have lost seven straight and 13 of their last 14 games.
Aaron Harang (5-13) suffered his MLB-high 13th loss of the season after allowing four runs and six hits with 10 strikeouts in 7 1/3 innings. He is 0-9 over his last 13 starts.
Copyright 2009 by United Press International.