The rookie left-hander, who made the NL All-Star team, is 0-4 in five starts since beating St. Louis on Aug. 6.
Once the clear frontrunner for NL rookie of the year, he has just three wins in 12 starts since July 2.
He pitched well enough to win his last outing, allowing three runs two earned and six runs and struck out eight in 6 2-3 innings, but was on the short end of a 3-2 loss to Pittsburgh on Tuesday night.
“I made some good pitches, but they put just enough wood on some of them to drive in the runs they needed,” Willis said. “I like how we’re playing ball. We’re in every game down the stretch, and that’s all you can ask.”
On Saturday night, the Marlins defeated the Expos 14-4, remaining a game behind NL wild-card-leading Philadelphia, which beat New York 9-6.
The Expos fell to 11-7 in Puerto Rico, where they are playing 22 “home” games this season—after this three-game series, they play three games against the Chicago Cubs.
STANDINGS: Marlins - 3rd place, 12 GB, NL East. Expos - 4th place, 17 1/2 GB, NL East.
MARLINS PROBABLE STARTER: Willis (11-6, 3.39 ERA). The left-hander is 1-1 with a 7.88 ERA in two starts against the Expos this season.
EXPOS PROBABLE STARTER: Javier Vazquez (12-9, 3.24 ERA). In his last start, the right-hander was tagged for five runs and eight hits over eight innings of a 5-3 defeat at Philadelphia on Tuesday night. That loss snapped a streak of three straight starts in which he did not allow an earned run. Vazquez is 6-2 with a 4.07 ERA in 13 career starts against Florida.
OFFENSIVE LEADERS: Marlins - Luis Castillo, .322 avg. and 88 runs; Mike Lowell, 32 HRs and 105 RBIs; Juan Pierre, 58 SBs. Expos - Jose Vidro, .318 avg.; Vladimir Guerrero, 23 HRs; Orlando Cabrera, 71 RBIs, 87 runs and 22 SBs.
SEASON SERIES: Marlins, 12-6.
STREAKS AND NOTES: Marlins - 2B Castillo is hitting .389 (14-for-36) in his career against RHP Vazquez. … Left-handed batters are hitting just .192 against LHP Willis this season. … 1B Derrek Lee has 28 homers on the season, a new career-high. Expos - After pitching eight innings in his last start, RHP Vazquez has pitched 200-plus innings for four straight seasons. … OF Guerrero is hitting .379 against left-handed pitchers this season. … RHP Vazquez is 3-7 with a 3.50 ERA in 14 road starts this season.
ROAD/HOME RECORDS: Marlins - 31-39 on the road; Expos - 47-24 at home.
INJURIES: Marlins - 3B Lowell (thumb), 15-day DL; LHP Armando Almanza (shoulder), 60-day DL; RHP Toby Borland (appendix), 60-day DL; RHP A.J. Burnett (elbow), 60-day DL; RHP Kevin Olsen (concussion), 60-day DL; RHP Tim Spooneybarger (arm), 60-day DL. Expos - OF Guerrero (knee), day-to-day; C Michael Barrett (hip), 15-day DL; RHP Orlando Hernandez (shoulder), 15-day DL; LHP Scott Stewart (appendicitis), 15-day DL; RHP Claudio Vargas (shoulder), 15-day DL; RHP Tony Armas Jr. (shoulder), 60-day DL; RHP Dan Smith (shoulder), 60-day DL; 3B Fernando Tatis (chest), 60-day DL.