The Cardinals bolstered their bullpen for the pennant chase, acquiring left-hander Zach Duke from the White Sox for a minor league outfielder.

Duke has appeared in an AL-leading 53 games this season and is 2-0 with a 2.63 ERA. The 33-year-old has 42 strikeouts in 37 2/3 innings.

The White Sox get 23-year-old outfielder Charlie Tilson, who's batting .282 with four homers, 34 RBIs and 15 stolen bases at Triple-A Memphis.