Anibal Sanchez will be the fifth starter, and he's scheduled to make his first appearance on April 9, at Philadelphia.
Because of off-days on April 6 and April 10, there was flexibility to go with a four-man rotation until April 15. But Sanchez now will fall into the fifth slot.
"We're not skipping anybody," manager Ozzie Guillen said. "Raining or not raining, whoever is scheduled to pitch that day is going to pitch. I'm not going to skip anybody."
Sanchez had a strong outing on Thursday, giving up one run on two hits in five innings in Miami's 3-1 win over the Cardinals at Roger Dean Stadium.
The Marlins' rotation will be Josh Johnson going in Wednesday's opener with the Cardinals at Marlins Park. On April 5, Mark Buehrle will start at the Reds. Ricky Nolasco will go on April 7 and Carlos Zambrano on April 8 in Cincinnati.
Sanchez is lined up for the series opener at the Phillies.
The Marlins will next use Sanchez either Tuesday or Wednesday in a Minor League game, before he gets ready for the regular season.
With an off-day on April 10, Johnson will get two extra days of rest after going on Opening Night. The right-hander, who missed most of last season with right shoulder inflammation, will make his second start on April 11 at Philadelphia.
"I don't need JJ in April," Guillen said. "I need JJ in September."
Sanchez, too, is being monitored closely. He missed time early in Spring Training with soreness behind his right shoulder. He threw 71 pitches on Thursday.
Sanchez said the Marlins' retractable-roof ballpark will be a benefit because it will take away stifling heat, as well as eliminate rain delays.
"We're going to have more energy, and not have any more games over 110 degrees," Sanchez said. "This season is going to be a nice season for everybody. We're going to have more energy. We lost a lot of energy last year.
"Rain delays are hard for everybody. It's harder for pitchers. Last year, I had three games where I was ready. I threw my last pitch and was ready to go straight to the game, and we had to stop for like 2 1/2 hours, two hours. Then you had to warm up again."