PORT ST. LUCIE — It’s still Johan Santana’s Opening Day start to lose.

Though Terry Collins is developing a contingency plan in the event Santana isn’t ready for April 1 at Citi Field against the Padres, the Mets manager yesterday said the lefty remains his top choice.

If Santana isn’t ready, Collins said he likely would give the ball to Jon Niese for the opener.

“If [Santana] is not ready for Game 1, I think he will be ready for Game 4,” Collins said.

PHOTOS: METS SPRING TRAINING

Santana, who is building up strength in his shoulder, participated in a long-toss session yesterday and likely will throw batting practice on Tuesday.

The Mets hope to get Santana pitching in an exhibition game by March 10 or 11.

* Lucas Duda was absent from the lineup in yesterday’s 6-2 win over the Tigers because of an undisclosed medical issue, but said he expects to play today against the Marlins.

“There is nothing wrong,” Duda said. “I went to the doctor and everything is fine.”

* Lefty Aaron Laffey pitched 1 2/3 shutout innings in relief yesterday and could join the pool of pitchers competing for the sixth spot in the rotation, should a starter be injured, according to Collins.

Jenrry Mejia, J

eremy Hefner and Collin McHugh are the other pitchers in that mix.

* Daniel Murphy began swinging a bat for the first time since straining a rib muscle last month, but won’t play in an exhibition game for at least another week, according to Collins.

* Pedro Feliciano resumed throwing from a mound, attached to a portable heart monitor. The veteran lefty was recently diagnosed with a genetic heart disorder, but is cleared to pitch.

* Collins praised his mentor Jim Leyland for bringing Justin Verlander and Prince Fielder, among the Tigers stars, on the two-hour bus trip from Lakeland. The manager then said jokingly that opposing teams must be calling general manager Sandy Alderson to complain the Mets aren’t playing their starters.

“Little do they know they are playing,” Collins said.