PORT ST. LUCIE, Fla. -- Relax, the Mets say. It's only Spring Training.

No worries down here in Florida, where palm trees dot the area surrounding Tradition Field. No worries here, where the stadium's most prominent feature isn't a scoreboard, but a tiki bar down the left-field line. Shoes and shirts may be required around Mets camp, but little else.

Got an injury? Take a day off. Maybe even two. Any team will tell you there's no need to push it -- not here, where the sun still shines and the games don't matter.

So really, there was no need for Luis Castillo to return to active duty with the Mets until he was completely ready. And once that happened, there was no need for him to sprint down the line on the first ground ball he hit, risking injury to his surgically repaired right knee -- or at the least, risking another few days on the bench.

But no worries. Not here.

"I always try to play hard," Castillo said. "If something happens, it happens."

Nothing happened this time -- Castillo was out by a hair -- and the Mets can only hope that's a trend. Despite his looming knee injuries, the Mets signed Castillo to a four-year deal worth $25 million in the offseason, and now need him to be their starting second baseman. That means all season long, with no worries and no excuses.

And that just might be the greatest challenge of all.

"He's OK right now, and I hope and pray that he stays healthy," Mets manager Willie Randolph said. "But I don't know. He got off to a slow start physically, but hopefully it's the right time for him to get going a little bit. Luis has had a history of being dinged up, but we'll see if he stays healthy for us all year."

His right knee was a problem last summer, but only to a degree. Though Castillo limped around the clubhouse and took his fair share of sick days, he shined on the field. Nearly all evidence of his balky right knee disappeared, replaced by slick double plays and smart hit-and-runs.

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Yet the injury bothered him. It irked him so much, in fact, that he underwent offseason surgery to clean debris from his knee. That procedure was intended to make him whole again, to make him normal.

And perhaps it worked -- though the Mets won't be convinced just yet. Castillo didn't show up to camp last month in any condition to play, and ultimately needed five weeks before he could make his Grapefruit League debut on Saturday.

But no worries here. No regrets.

"I feel so good," Castillo said. "I feel happy because I think I made the right decision, honestly. I felt so good, and for a long time, I didn't feel like that."

That's a common sentiment around Mets camp, where the injuries seem to outnumber the worries. A few extra days off can make a disproportionate difference.

Just ask first baseman Carlos Delgado, who spent more than a week glued to the bench with an impingement in his right hip. Smart move, if his opposite-field home run in Saturday's game was any indication.

"I'm glad I took the time," Delgado said. "I just wanted to make sure I was in good shape before I went out there and tried to do a whole bunch of stuff."

The Mets need Delgado, for certain, but they may need Castillo even more. After all, they've entrusted the immediate future of their middle infield to him, hoping he and shortstop Jose Reyes can form a potent tandem both on the field and at the plate.

They've seen it happen before. After the Mets traded for Castillo last summer, they watched as he hit .296 with 10 stolen bases, vexing pitchers and helping Reyes wreak havoc. That Reyes stole a Mets-record 23 bases in August -- Castillo's first month with the team -- was no coincidence.

"He's steady," Randolph said. "His track record is pretty consistent, for the most part. Although he was hampered last year, I still thought he did a nice job for us. Luis has been around the block many times, and he knows how to handle himself."

Yet consider also that one of Castillo's infield backups, Ruben Gotay, remains shelved indefinitely with a sprained right ankle, and another, Jose Valentin, needs to prove he's healthy enough just to make the team. The mounting injuries are disconcerting, especially because Castillo, who never went on the disabled list in 2007, missed 27 games.

But no worries. He finished Saturday's game with that first frenzied groundout and a pair of walks -- and more importantly, with a clean bill of health. Castillo plans to play on Sunday, and perhaps even Monday. Perhaps even beyond.

"Today, I feel so different, and that's good for me out of surgery," he said. "That's good news for me."