JUPITER, Fla. -- Shortly after the travel squad left the Mets' Spring Training complex at Port St. Lucie, Fla., on Wednesday, Johan Santana marched outside to begin some light work. One day after his first Major League start in 18 months, Santana was planning nothing more significant than a massage.

"No matter if you've had surgery or not, you're going to be sore the next day," manager Terry Collins said. "Everybody is after they pitch. So I'm sure he had some stiffness, but he felt good."

A far more important test will come Thursday, when Santana attempts to throw again. That could come in the form of playing catch off flat ground or a full bullpen session, depending on the level of soreness in his shoulder.

"It's possible his workload will be tailored to how he feels," general manager Sandy Alderson said. "But we won't know that until [Thursday]."

Throwing 29 pitches Tuesday afternoon against the Cardinals, Santana took the mound in a Major League game for the first time since undergoing left shoulder surgery in September 2010. He is scheduled to start again on Sunday, keeping him in line to pitch Opening Day against the Braves on April 5.

Beato scheduled for MRI

JUPITER, Fla. -- A day after cutting short Tuesday's relief appearance due to right shoulder discomfort, Mets reliever Pedro Beato was scheduled for an MRI on his ailing arm.

The Mets should know the results of that test by Wednesday evening, after Beato left Tuesday's game due to muscle stiffness. Even if he were healthy, Beato would be on the bubble of a bullpen competition that has as many as 10 competitors vying for two open spots.

One of Beato's main challengers on that front, Bobby Parnell, bounced back from two rough outings over the weekend to pitch a perfect inning Wednesday.

"Bobby Parnell wants to make this team in the worst way," manager Terry Collins said. "One of the things I saw [Wednesday] was great command."

Niese focused on improving changeup

JUPITER, Fla. -- As a young pitcher, Jon Niese turned heads with his curveball, which Jose Reyes once compared to that of Barry Zito. As he began to mature, Niese started leaning more heavily on his cut fastball, which former catcher Rod Barajas once called his best pitch.

Now, Niese wants to improve his changeup in just the same way. Niese focused on that offering in particular on Wednesday, firing two scoreless innings against the Marlins in Jupiter.

"That's the pitch that I have less experience with, so I'm definitely going to be working on that a lot more, just so that I can master it like I've done with my cutter," Niese said. "My cutter was a real good pitch for me last year. I think my changeup could be devastating if I master it."

Though both manager Terry Collins and pitching coach Dan Warthen urged Niese to throw curveballs more often last season, chastising him at times for shying away from his best pitch, both are happy to see the progress with his changeup.

"I think the changeup's the best pitch in baseball," Collins said. "If you're a pitcher, you should have a changeup in your repertoire. If you can locate your fastball as Jon can and you've got a change to go with it, you're going to be pretty effective."

Worth noting

• Third baseman David Wright continues to receive treatment on his sore left rib cage, but will not appear in a Grapefruit League game until after the weekend. "He's progressing, which is a good sign," general manager Sandy Alderson said. "There hasn't been a setback."

• Justin Turner finished 3-for-3 with his first home run of the spring on Wednesday. Turner is in line to break camp as the Mets' primary backup at first, second and third base.