MIAMI -- Following Tuesday's Mets loss to the Marlins, manager Jerry Manuel lauded Mike Pelfrey's ability to remain strong this late in September. Such stamina, Manuel noted, is one of the final assets a young pitcher develops before turning into a star. Remaining strong for six months has always been one of baseball's greatest challenges.

Pelfrey has accomplished it. Jon Niese has not.

Though Niese has insisted throughout September that he still feels plenty strong, the numbers have proven otherwise. Wednesday's loss, a 7-5 defeat to the Marlins at Sun Life Stadium, dropped the rookie left-hander to 1-3 with a 5.56 ERA in September, tarnishing what otherwise has been a fine rookie season.

The numbers don't matter, of course, so consider it a learning experience. Niese will.

"This time of year is a good time to battle through my struggles," Niese said. "Obviously, I don't want to struggle, but when I do, I'll try to work to it and fix what I wasn't able to do."

Walking three of the first six batters he faced in Wednesday's game, Niese allowed a run-scoring single to Dan Uggla, a bases-loaded walk to Mike Stanton, a two-run double to Wes Helms and an RBI base hit to Brad Davis -- all in the first inning. Though Niese settled down enough to last 5 2/3 innings, he also walked a career-high six batters and allowed 13 baserunners.

"I had no fastball command," Niese said. "There's really no excuse for it. I should be throwing strikes. That's what I'm out there to do, and it's unfortunate that I walked too many guys."

Twice, the Mets battled back, scoring a key run on Carlos Beltran's solo homer off Marlins starter Alex Sanabia in the fourth inning, then two more on Josh Thole's bases-loaded walk and Chris Carter's RBI groundout against a shaky Marlins bullpen in the eighth. But the Fish did not break.

Instead, Uggla made a fine play to wrap up Clay Hensley's fifth save, pushing the Mets deeper into fourth place than they already were.

"That last one was a lot of fun, it kept the run from scoring," Uggla said. "Kept the save for Clay. It was a lot of fun."

For the Mets, though, this was not a lot of fun. Not even a little bit. Though Wednesday marked their first day officially eliminated from the playoff race, the Mets arrived at Sun Life Stadium aiming to accomplish something. September, as Niese noted, has become a time for them to develop.

And, to be fair, some of them did. Beltran, for example, constructed his most complete offensive game of the season, finishing a double shy of the cycle, scoring two runs, driving in another and hitting the ball hard in each of his five plate appearances. Batting .211 as recently as Sept. 3, Beltran is now up to a season-high .246.

"He's swinging the bat well," Manuel said. "I think Carlos is probably getting ready to have a big year next year. I see some improvements."

"I felt like I had four or five quality at-bats," Beltran said. "I was able to see the ball good and hit it hard anywhere. It's a good feeling when you feel like that at the plate, that you have a chance every time."

As recently as last month, Niese could say the same about his every appearance on the mound. Once nearly guaranteed to give the Mets a quality start, Niese has lost that quality control. Mainly because he's lost his control.

The Mets suspect it's because of fatigue, and that makes sense. Niese has already thrown dozens more innings this season than he did a year ago, when he missed much of the summer with a hamstring injury. Tiring at season's end is only natural.

"He has to learn to kind of manage that," Manuel said. "He has to learn to prepare for that."

"It's tough this late," Niese said. "I've never really battled this late in a season. Obviously, I want to stay in shape, stay in good condition and battle out there every start."

As it stands, Niese will make two more starts, including the season finale a week from Sunday at Citi Field. And he has high hopes for them.

Put simply, Niese wants to head into the offseason with a better taste in his mouth than this.