Kevin Appier (10-8) allowed two runs, six hits and four walks in 6 1-3 innings for the win, his second straight following a five-game losing streak.
Chicago, which has lost eight of 12, drew just 30,019 for the start of the big three-game series.
White Sox designated hitter Harold Baines, acquired Saturday from Baltimore, was given a 2-minute standing ovation before his at-bat in the second inning. Baines, in his third stint with the White Sox, was 1-for-4.
Mike Sirotka (9-9) didn't allow a runner past first base in the opening five innings.
Sirotka gave up three runs and five hits in seven innings, striking out seven.
Pinch-hitter Matt Stairs added an RBI groundout off Billy Simas in the eighth for a 4-2 lead.
Jason Isringhausen pitched the ninth for his 25th save in 30 chances.
Valentin's two-run homer in the third followed Ray Durham's walk and put Chicago ahead.
Carlos Lee hit a leadoff single in the seventh and Appier's 2-2 pitch appeared to hit Chris Singleton in the left foot. Singleton walked to first, but after a conference with third-base umpire Gerry Davis, plate ump Rich Rieker ruled it a wild pitch.
Singleton struck out on the next pitch, Charles Johnson walked and Mike Magnante relieved, getting Durham hit into a double play.
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