MLB: Chicago Cubs 9, Milwaukee 5

CHICAGO, July 2 (UPI) -- Derrek Lee drove in a career-high seven runs Thursday with two of Chicago's four home runs, boosting the Cubs to a 9-5 decision over Milwaukee.

The explosion of long balls came in the opener of a key series, in which the Cubs hope to make a big gain in the National League Central race. Milwaukee slipped back into a first-place tie with St. Louis, Cincinnati is two games behind, the Cubs are 2 ½ back and Houston trails by three.

Lee opened the onslaught with a three-run homer in the first inning and Jake Fox contributed a solo shot later in the frame.

After Geovany Soto homered to lead off the Chicago fourth, Lee belted a grand slam to left-center. It was the 20th multi-homer game of Lee's career.

Mike Cameron and Prince Fielder hit home runs for the Brewers, who lost their second straight.

Ryan Dempster (5-5) benefited from the power performance, getting the win by giving up three runs on eight hits in 6 2/3 innings. He struck out nine.

Seth McClung (3-2) made only his second start of the year for Milwaukee and was roughed up for seven runs in just 3 1/3. He has made 28 relief appearances this season.