The Marlins (6-16) were swept in a three-game series by Colorado at home over the weekend and have lost six of their past seven contests.
Willis has made five starts this season, but only earned decisions in two of those outings. The Marlins are 1-4 when he starts.
Willis (1-1, 3.13 ERA) lost to the Cubs last Tuesday, giving up three runs and five hits to lose an April start for the first time in his career. While he is 9-1 in April, Willis is just 8-6 in May.
This will be his 13th career start against Philadelphia, the most against any team. Willis is 5-3 with a 2.96 ERA against the Phillies.
“Dontrelle is a winner. You watch Dontrelle pitch and you understand why he’s successful,” Marlins manager Joe Girardi said. “He does all the things that you have to do. He does everything right and everything it takes to be a winner.”
Florida lost 3-1 on Sunday to the Rockies, their 11th loss by two runs or fewer. The Marlins struck out 12 times and have fanned 135 times in their last 13 games.
“You’ve got to put the ball in play,” Girardi said. “We don’t have experienced guys, and it’s going to take time. There are going to be days when you don’t strike out a lot. It’s going to take time, because they are young, they are overaggressive at times, they haven’t seen the pitchers.
“It’s something you have to deal with. You have to find a way to get better at it, and we will. I think a lot of it is just time.”
The Marlins are only 2-7 at home and have the fewest wins in the National League. Their April record was the third-worst in franchise history, trailing only 1995 (1-4) and 1999 (6-17).
Philadelphia (10-14) hasn’t been much better.
The Phillies ended a three-game losing streak by beating Pittsburgh 5-1 on Sunday. It was the first time in four games Philadelphia scored more than three runs.
Ryan Madson (2-1, 8.05) starts for the Phillies on Monday. He has a winning record this season thanks to excellent run support, as Philadelphia has scored 29 runs in his four starts.
Madson is 0-2 with a 2.25 ERA in 17 relief appearances against the Marlins.
Miguel Cabrera is the only Marlins batter to face Madson more than twice, with two hits and no RBIs in 13 at-bats against the 6-foot-6 right-hander.
The Marlins and Phillies split two games in Philadelphia two weeks ago, with one contest postponed due to rain. This series wraps up Tuesday with Philadelphia’s Jon Lieber scheduled to face Florida left-hander Scott Olsen.