Willis (17-8) lasted just five innings while giving up two runs and five hits and walking five. He joined St. Louis' Chris Carpenter as the only 17-game winners in the major leagues.
Carlos Delgado was 3-for-4 with two RBI for the Marlins, who concluded a season-long 13-game home stand by going 9-4. The win moved Florida to within one-half game of the NL wild card-leading Philadelphia Phillies.
Edwin Jackson (0-1) allowed three runs and five hits over 4 2/3 innings to take the loss. Jackson, who also walked five, was called up earlier in the day to start for Odalis Perez after the veteran was placed on the 15-day disabled list with a strained right oblique muscle.
Jose Cruz Jr. and Dioner Navarro had RBI singles for the Dodgers, who lost three of the four games in the set.