Atchison, 37, opened the season with New York, posting a 4.50 ERA in 19 appearances. He then went on the disabled list in mid-May with numbness in a finger stemming from a bone spur in his elbow.
He returned to the DL on June 19 after straining his groin during warmups and pitched a scoreless inning on a rehab assignment for Double-A Binghamton on Thursday. Sunday morning, he drove from Binghamton to Syracuse, then flew to LaGuardia Airport in New York, then to Pittsburgh. He arrived at PNC Park two hours before the game.
"It's good to be here," Atchison said. "Better than Binghamton."
Valdespin, hitless in his last 11 at-bats and 2-for-36 before the demotion, has a .188/.250/.316 slash line this season for the Mets. He hasn't started a game since June 22.
"It's hard for a young player who has pretty much spent his whole career as an everyday player to come up and play, maybe, once a week and then come off the bench and hit," Collins said. "It's very difficult. So he's got to go get some playing time. He's got to get his swing back. Certainly get back in the lineup. If he's going to come back, at least he's got to get some at-bats."
Valdespin has played all positions in the outfield, second base and shortstop this season for New York, and Collins said he'd like to see him do the same in Las Vegas.
Steven Petrella is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.