SAN DIEG0 -- The Mets' need for starting pitching created by the season-ending injury to Jon Niese on Wednesday briefly became more acute Wednesday night when they learned Mike Pelfrey, the scheduled starter for their game against the Padres on Saturday night, wouldn't accompany the team here, instead remaining in New York with his wife, Angela, awaiting the birth of their first child.

The situations were resolved in a period of hours Thursday afternoon. The club decided Bobby Parnell would move from the bullpen to the rotation and replace Niese for the remainder of the season. And Pelfrey and his wife became parents of a 7-pound, 14-ounce son. Pelfrey was named to start Monday against the D-backs. His son was named Chase Michael.

The Monday assignment would have gone to Niese, but he tore his upper hamstring tendon from the bone Wednesday and underwent surgery Thursday afternoon. The club has assigned him to the 60-day disabled list.

The Mets had prepared Parnell for his first big league start -- as much as they could, given the time element -- by having him pitch three innings in relief Wednesday afternoon. He had pitched more than an inning twice in his first 41 appearances. Then he pitched two innings Monday in the poor start by Nelson Figueroa and three innings, for his first big league save, in what might be his final relief appearance.

"I know I'm starting Saturday. After that, they'll let me know," Parnell said. "I'm excited about it."

Parnell had started 92 times in 94 Minor League appearances before pitching in relief exclusively in the big leagues. "I've kept an open mind about [his role]. I don't mind either way," he said.

"This will give us a good read on Bobby Parnell," manager Jerry Manuel said. "If he does well, it would give us something to think about."

To take Niese's place on the roster, the Mets purchased the contract of veteran right-handed pitcher Elmer Dessens from Triple-A Buffalo. He was to join them in time for the first game of the four-game series in San Diego.

Dessens, 38, was with the Mets from June 22 through July 30. He pitched 12 1/3 innings in nine appearances -- eight of them losses, allowing five runs, nine hits and five walks. He struck out six. He had no decisions and a 3.65 ERA and allowed two of his 10 inherited runners to score.