Hunter Pence hit two home runs and drove in a career-high five runs to back Rodriguez and power the Houston Astros to a 6-1 victory Friday over the Cubs, now 13-21 against southpaw starters.

The Cubs began the day with a 2 1/2-game lead in the National League Central over the Milwaukee Brewers, aided by a win over Brewers lefty Manny Parra on Thursday.

Rodriguez (7-13) limited the Cubs to four hits and two walks over six shutout innings, striking out five.

Before the game began, Chicago bolstered its pitching staff for the final month by acquiring right-hander Steve Trachsel from the Baltimore Orioles in exchange for two Minor Leaguers. What the Cubs will do with Trachsel has yet to be announced, but one option may be inserting him into the rotation. Sean Marshall could be on the bubble.

Marshall (7-7) exited after 3 2/3 innings Friday, giving up four runs on five hits and four walks. For the month, he's 2-3 with a 6.18 ERA. The left-hander threw 84 pitches, 31 of those in the first inning.

Pence was involved in all of the Astros' scoring. He walked to lead off the game, and scored one out later on Lance Berkman's double.

Ty Wigginton reached on a fielding error by third baseman Aramis Ramirez to open the Astros' fourth, and Chris Burke singled. Two outs later, Pence launched his 13th homer into the left-field bleachers to go ahead, 4-0. Pence added a two-run homer with two outs in the sixth for his first multi-homer game.

Despite the loss, the Cubs will be in first place on Sept. 1. They were 7 1/2 games back on June 1.

This story was not subject to the approval of Major League Baseball or its clubs.