Among four recalled from Double-A Altoona was All-Star left-hander Jeff Locke.
Locke and Grilli will both immediately jump back on the pennant-race treadmill. Locke is scheduled to start the middle game of this weekend's series in St. Louis with the Cardinals. Grilli will pitch in a few "non-leverage outings," in manager Clint Hurdle's words, then reclaim the closer's role.
Also recalled from Altoona was pitcher Jared Hughes, outfielder Andrew Lambo and catcher Tony Sanchez.
The moves put the Pirates' active roster at 32.
Grilli started Saturday and Monday for the Curve, pitching one shutout inning on both occasions. He was due to pitch an inning out of the bullpen in the Indians' playoff game Wednesday in Durham, but he struck out the side in Monday's outing, and the staff felt no need to extend his rehab.
"In that second outing, he really ramped it up," Hurdle said. "Now with the challenge of facing Major League hitters and the adrenaline that goes with it, we'll have a much better feel [for where he's at]. Eventually, the plan is to transition him back to the closer's role."
Grilli led the National League with 30 saves when he went down with forearm tightness on July 23. In his absence, Mark Melancon has converted eight saves in nine opportunities.
"I'm not here for myself. I've said that all year," Grilli said. "I'll pitch when they give me the ball. Mark's been doing a great job. We're all in this for the same thing.
"If I want to get out big league hitters, I've got to face them," added Grilli, echoing the sentiment that there was nothing to be gained by having him follow through on that third planned rehab outing. "I think I showed my arm is where it needs to be. There was not much else to prove."
Locke -- due to toss a bullpen session prior to Tuesday night's game as a warmup to his Saturday start at Busch Stadium -- returned with the same positive outlook. He had skipped a turn and was optioned to Altoona as a roster convenience after failing to last past the fourth inning in three straight starts.
"Plan is to jump right back on, go out there, give us a chance to get on top and hold them to minimal offense," Locke said.