Two strikes from what would have been his 31st save, Grilli threw one pitch to pinch-hitter Steve Lombardozzi, grimaced, motioned to the Pirates' third-base dugout for trainer Todd Tomczyk and minutes later walked off the field clutching his right elbow.
"We'll wait and see where it all goes, but right now, it's right forearm discomfort," said Pirates manager Clint Hurdle, cautioning reporters. "And that's all I've got, so no sense asking me anymore about it. We're not running him out of here. We'll see how he feels tomorrow."
"Praying everything is all right," said Andrew McCutchen, whose pair of two-run homers had fueled the victory.
McCutchen lockers next to Grilli, who was sitting with a towel wrapped around his right forearm, staring down and into his own locker. McCutchen spoke through a forced smile, and when reporters receded, walked up to Grilli and draped an arm around his shoulders.
In the event of Grilli's absence, closing duties would fall to fellow All-Star Mark Melancon, who has excelled as the Pirates' setup reliever and served as the man at the end of Houston's bullpen in 2011.