Ryota Igarashi pitching the 8th inning before leaving the game...

Ryota Igarashi pitching the 8th inning before leaving the game because of injury. (April 20, 2010) Credit: David Pokress

The numbness in Ryota Igarashi's left hamstring did not improve overnight, so after an MRI Wednesday the Mets placed the righthanded reliever on the 15-day disabled list.

Manny Acosta, a righty whom the Mets picked up from the Braves on waivers at the end of spring training, was called up from Triple-A Buffalo. Acosta will replace Igarashi on the roster - but not in the eighth inning, which Igarashi had begun to call his own.

Manager Jerry Manuel said last night that Fernando Nieve and Pedro Feliciano would share eighth-inning duties for now. He also teasingly threw out the option that Jenrry Mejia could receive an upgrade in responsibility now that his 20-year-old feet are wet.

Mejia went into the game against the Cubs with an 0-1 record and 2.00 ERA in eight appearances. Manuel has attempted to baby him as much as possible, but sometimes circumstances have forced the neophyte into important moments. They may increase.

"I think he has shown that there's some situations that he can handle," Manuel said. "He's throwing strikes, for the most part. He's still progressing, developing. If we had a situation where we had used people and he was there, I wouldn't be afraid to give him the opportunity."

Igarashi was injured in the eighth inning of Tuesday's 4-0 win over the Cubs when he attempted to field a leadoff bunt. He pitched to two more batters before he had to come out.

The Mets called it a "moderate" strain. Igarashi said he had a similar but worse strain two years ago and missed a month. He said he didn't think he would need that long this time.

Igarashi recently began to show the kind of stuff that caused the Mets to give him a two-year contract. He has a 1.35 ERA in seven outings.

"Of course there is some frustration," Igarashi said through his translator. "I started to feel that I was pitching [well]."

Igarashi was replaced Tuesday by Nieve, who appeared in 10 of the Mets' first 14 games. Nieve went into last night 1-1 with a 4.82 ERA. Manuel said he thinks Nieve has proved to be a rubber-armed type who can handle a heavy workload.

"He seems to be a guy that really is made for that type of role," Manuel said. "I think for him and a lot of guys, the more you get on the mound, the better for you, the better you become."

Acosta, 28, was 0-1, 2.16 at Buffalo. He gave up a two-run homer to Alfonso Soriano in his Mets debut.