PORT ST. LUCIE, Fla. -- Since high school, Matt Harvey has drawn a guide line on the pitcher's mound before every inning, digging his cleat in the dirt perpendicular to home plate. The line helps him keep his mechanics fluid, preventing him from crossing his arm across his body as he throws.

Harvey paid particular attention to that issue during his bullpen session this week, then focused on those improvements throughout Thursday's Grapefruit League start against the Marlins. The results were 4 1/3 scoreless, hitless innings.

"He's on a mission to be real good," manager Terry Collins said. "When you bring something up to him, he applies himself."

Harvey mowed down 13 of the 14 Marlins batters he faced at Tradition Field, the lone exception coming on shortstop Omar Quintanilla's fielding error. Showcasing an improved changeup from his previous outings, Harvey felt as sharp as he looked.

"He was definitely locked in," catcher Anthony Recker said. "Over on the mound on the side, warming up, he was locked in, throwing strikes down in the zone. And then he went out there and took it out into the game, which is really impressive."

Partially because his mechanics were out of whack, Harvey said, he bounced several changeups in his previous start against the Marlins. Not so on Thursday, which is a good sign for the young right-hander. Minor adjustments could play a significant role in how he adapts during his sophomore season.

"Scouting reports are out now," Collins said. "Films, scouting reports, they're all over the place. So now it's about making adjustments and making pitches."

Wheeler making progress in rehab

PORT ST. LUCIE, Fla. -- Top pitching prospect Zack Wheeler continues to make slow but steady progress in his rehab from a strained right oblique muscle, climbing atop a mound Thursday for the first time since injuring himself on Feb. 27.

With a small gaggle of teammates and coaches looking on, Wheeler threw a 30-pitch bullpen session at an estimated three-quarters effort.

"Honestly, today is probably the first day that it's 100 percent," Wheeler said of his oblique, which he injured during pitcher's batting practice. "Leading up to this day, it was getting better every day. I'll continue to get treatment for it probably throughout Spring Training, a little preventative thing."

The Mets have no intention of rushing Wheeler back into game action, considering he will not break camp with the big club anyway. Still, the right-hander is anxious to make his second career Grapefruit League start after dazzling with two scoreless innings in his first one.

Said Wheeler: "Everybody at this point wants to face live hitters and be in games."

Francisco hoping to make debut Saturday

PORT ST. LUCIE, Fla. -- Closer Frank Francisco aims to step on a mound on Saturday for the first time this spring. His readiness for Opening Day is not so clear.

"We never know," Francisco said. "I might give you a little surprise. I know I'm going to be OK. If I [miss] a few games, maybe five or six games, it's for my own good. I know I can go out there and rush a little bit, but I'm risking taking another step back. That's what I don't want."

Battling inflammation in his right elbow, Francisco continued his long-tossing program Thursday at distances up to 130 feet. If Francisco is not ready to pitch on Opening Day, Bobby Parnell will serve as closer.

Francisco underwent surgery in December to remove a bone spur from his elbow. He began throwing off flat ground early in February before discovering the inflammation.

"I just feel like I've got to get my strength, throw a little more maybe, get my power back," Francisco said. "I feel like I'm not loose yet, like I don't have power in my whole body. I feel like I don't have my release point yet. That takes a while."

Mejia can return to camp with no limitations

PORT ST. LUCIE, Fla. -- Right-hander Jenrry Mejia has been cleared to return to Mets camp with "no limitations," according to manager Terry Collins, after his pre-spring physical raised a red flag.

Mejia, 23, left camp earlier this week to receive testing on a medical issue unrelated to his pitching arm. He spent two nights in New York before learning that team doctors cleared him to return to camp.

Mejia has appeared in one Grapefruit League game, giving up five runs in his only inning. He reported to camp more than a week late due to visa issues in the Dominican Republic, and is scheduled to begin the regular season in the rotation at Triple-A Las Vegas.

Worth noting

• Second baseman Daniel Murphy (strained right intercostal muscle) hopes to make his Grapefruit League debut sometime next week, though he is hesitant to put a firm timetable on it. Murphy, who has been taking soft toss swings in an indoor batting cage, remains confident that he will be ready to go well in advance of Opening Day.

• Outfielder Kirk Nieuwenhuis (bone bruise in left knee) ran in an indoor pool Thursday, and said his leg was feeling significantly better. Nieuwenhuis remains on track to return to the lineup at some point next week.

• Tickets for All-Star FanFest and Taco Bell All-Star Sunday will go on sale Saturday at 10 a.m. ET, at mets.com, AllStarGame.com or at the Citi Field box office. FanFest will run from July 12-16 at the Jacob K. Javits Convention Center in Manhattan. All-Star Sunday includes the SiriusXM All-Star Futures Game and the Taco Bell All-Star Legends & Celebrity Softball Game.