With the Marlins off, Mitre pitched in a Triple-A game on a back field at the Roger Dean Stadium Complex.
Facing Cardinals' Minor Leaguers, Mitre gave up one run on three hits in 4 1/3 innings, striking out six and throwing 45 of his 59 pitches for strikes.
Two of the three hits were off-the-end-of-the-bat rollers that landed for infield singles. And Mitre never reached a three-ball count.
"Not bad," Mitre said, summing up his outing. "I threw breaking balls and changeups, and I was trying to work on my pitches.
"My curveball is real good right now, and my changeup I threw for strikes. I'll take it."
The Marlins have yet to announce their fifth starter, and the club won't need one until April 10 because of an April 5 off-day.
Mitre is the clear favorite to get that nod. Yusmeiro Petit, who is another possibility, also threw on Wednesday, tossing 27 pitches in two shutout innings.
Reliever Henry Owens, a candidate to close, gave up one hit in two-thirds of an inning, throwing 11 total pitches.
Also seeing game action for the first time since March 10 was shortstop Robert Andino. Andino was involved in a collision with Alfredo Amezaga on that date, and he has been nursing a sore back since.
Leading off for five innings, Andino had one single in five at-bats. He played the field for five innings, but afterward said his back felt a little tight and he's now about 85 percent.
The Marlins have lined up their starting pitching for the final 10 exhibition games heading into the April 2 opener in Washington at RFK Stadium.
One reason Petit threw two innings on Wednesday is because he will start on Sunday against the Red Sox in Fort Myers, Fla. Since Petit is going on short rest, he wasn't pushed longer in the Minor League game.
On Thursday, Dontrelle Willis will start against the Cardinals, Anibal Sanchez will face the Dodgers on Friday and Scott Olsen will go on Saturday against the Mets. Also, Petit goes on Sunday, and Mitre will pitch Monday against the Cardinals. Also that day, Ricky Nolasco will start in a Minor League game.
On Tuesday, a yet-to-be-named Minor Leaguer will start in the meeting with the Orioles in Fort Lauderdale, Fla. Willis was in line to face the Nationals on March 28, but he will instead pitch in a Minor League game.
Willis will be the Opening Day starter in Washington, so the team doesn't want to showcase him against them next week. Willis also will be working on six days' rest that day, giving him another day before the season begins.
Olsen will start on March 29, and Petit will start against the Mets in the Grapefruit League finale on March 30. The Marlins take on the Reds in an exhibition game in Dayton, Ohio, on March 31, and right now, Nolasco is scheduled to pitch there, while Mitre is slated for a Minor League start the same day.
Joe Frisaro is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.