Facing prospects in the Mets' system, Willis gave up two runs on four hits with five strikeouts and a walk at the Roger Dean Stadium complex.
Willis' next appearance will be on Opening Day this coming Monday against the Nationals at RFK Stadium.
In all, Willis threw 72 pitches and came out of the game excited to get the season under way.
"It was very productive," said Willis. "I want to continue working and finish up strong, and get ready for the season. I feel really confident with my stuff. I was able to do some things I wasn't used to doing, like throwing breaking balls when the hitters are ahead, and cutting down the walks the best I can.
"I think I did a better job with that this spring, and hopefully it carries over."
Willis was 1-3 with a 4.58 ERA in five Grapefruit League starts. Counting his four innings on Wednesday, he logged 23 2/3 total innings and had 18 strikeouts to five walks.
Manager Fredi Gonzalez had Willis pitch in the Minor League game before the Nationals were in town. If it was any other team besides the club he will face on Opening Day, Willis would have thrown in Wednesday's Grapefruit League game.
"I feel really strong," said Willis, who took care of the Minor League players by buying them a meal. "This is as strong as I've felt in Spring Training, and hopefully my arm will continue to feel like that through the season."
Miguel Olivo caught Willis on Wednesday.
Between innings, Willis found himself signing about seven autographed baseballs for his Minor League teammates for a day.
Tankersley to DL: Early Wednesday morning, Taylor Tankersley was informed he will begin the season on the disabled list. By early afternoon, the lefty reliever was on the mound in game action for the first time this spring.
The 24-year-old lefty reliever threw one inning in a Double-A game against the Mets on a back field at Roger Dean Stadium. Tankersley gave up one run on two hits and logged 15 total pitches.
The most telling thing about the outing was the 2004 first-round pick came through the outing feeling fine.
Tankersley's next scheduled outing will be on Saturday in Jupiter, Fla. He won't fly with the team to Washington, so he will not be on hand for Monday's opener.
"It's tough, because I've never been part of Opening Day," Tankersley said. "But I'm going to be part of the team for 145 games."
A year ago, Tankersley opened the season in Double-A Carolina, and he was eventually called up in early June. He's been building himself back up from shoulder inflammation all spring.
The move has not been made official yet, but Tankersley will begin the season on the DL, retroactive to March 23. That means the earliest he can be reinstated will be on April 7.
Gonzalez, however, noted that the club isn't going to rush Tankersley, its top lefty setup reliever.
Until Tankersley is ready, Renyel Pinto will be the lone southpaw in the bullpen.
Reed to Triple-A: Eric Reed enjoyed a strong Spring Training, yet he found himself optioned Wednesday to Triple-A Albuquerque, clearing the way for Alejandro De Aza to win the center-field job.
While De Aza showed enough all-around skills to secure the position, Reed enjoyed his best big-league camp. Reed has one more option season, and he now goes back to Albuquerque after batting .351 (13-for-37) in 15 games.
Willis noted that Reed shouldn't be discouraged.
"Reed had a great spring as well," Willis said. "There were a lot of guys who had great springs, but unfortunately, it's the numbers game. You can't have four center fielders out there."
Gonzalez encourages players who don't make it to "prove us wrong."
"If you get sent down, prove us wrong," Gonzalez said. "There have been a lot Hall of Fame players who have been sent down, came back and had [great] careers."
Fish bites: While Jason Wood and John Gall are each candidates for the final position player spot on the roster, the Marlins may look at other options. A name worth watching is infielder Todd Walker, released Monday by the Padres. Walker would be a candidate to provide a lefty bat off the bench. ... Lee Gardner, who is competing with Nate Field for the final reliever spot, ran his scoreless-innings streak to 13 1/3 after a two-inning performance on Wednesday. With a split contract, Gardner would go to Triple-A if he doesn't make the club. ... Closer Jorge Julio is scheduled to arrive in camp on Thursday. Acquired Monday from Arizona, Julio has been getting everything in order before he headed to Florida. Initially, he was supposed to be in uniform on Wednesday. ... The Marlins on Friday will start Ricky Nolasco against the Mets at Port St. Lucie, and Sergio Mitre will get the call on Saturday when the team faces the Reds in Dayton, Ohio.
Coming up: The Marlins on Thursday will play their final home Spring Training game at Roger Dean Stadium at 1:05 p.m. ET. Anibal Sanchez gets the nod for the Marlins, while St. Louis is going with Kip Wells.
Joe Frisaro is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.