After Taijuan Walker hit Posey in the head with a 94 miles per hour fastball, AT&T park collectively gasped, and then booed, rightfully so.
Miller allowed three runs over 5 1/3 innings with five strikeouts and two walks.
Arizona improved to 7-2, matching its best start in franchise history.
While manager Bruce Bochy said following Monday's 4-1 victory that Posey was doing fine, the Giants planned to check in with him overnight and re-evaluate him Tuesday.
"Mark's a beast. I'll take him every day", Moore said. Posey got up on his own but exited the game, with Nick Hundley entering to pinch run and stay in the game behind the plate. This one looked like a mistake and that's exactly how Posey interpreted it. "Which is good news".
"It's a smart move, especially to have that one yesterday and as a catcher, you never know."
Posey already has begun exercising, and elevating his heart rate has not brought on any concussion symptoms, Bochy said. "At the end of the day, I just didn't make quality pitches". Panik came home as catcher Jeff Mathis scrambled to the backstop and threw to Walker covering the dish.
"That was fun", said Parker, who pumped a fist as he emerged from his head-first slide.
"Everybody realizes that that pitch got away from Taijuan, and I'm hoping that Buster's OK", Diamondbacks manager Torey Lovullo said.
It was the old "run thrown in", or RTI, as Tim Flannery called it, that the Giants used to their benefit on a couple of occasions in the 2014 postseason. It gave Moore all the support he needed, though the Giants tacked on another run in the seventh on Crawford's sacrifice fly deep into Triples Alley.
Pitcher Matt Moore was at the plate with the bases loaded and hit a weak dribbler up the first base line.
Cory Gearin struck out three straight batters to end the inning.