In a frightening scene at PNC Park, Piscotty lay motionless on the grass in left-center field for several minutes. He was strapped to a backboard and waved his left hand as he was driven away, eliciting a big cheer from the Pittsburgh crowd.
Piscotty has a bruise on his head and all tests conducted were negative, the Cardinals said. Cardinals manager Mike Matheny said Tuesday that Piscotty was released from the hospital with "a couple bruises, but overall everything checked out very clean."
In the bottom of the seventh inning, Josh Harrison of the Pirates hit a drive to the gap in left-center. Piscotty, playing left field, stumbled as he chased the ball. Bourjos, playing center, went to the ground as he made a lunging catch, and his left knee struck Piscotty square in the face.
Almost immediately, Bourjos began waving to signal that Piscotty needed medical attention.
"We couldn't hear each other," Bourjos said after the game, according to MLB.com. "The ball was just hit between us, and we both tried to make a play on it. The situation in the game, I think we both thought if the ball fell it might be the outcome of the game.
"You could just tell that Stephen wasn't right and that he needed some help."
Matheny gathered in the outfield, some kneeling in obvious concern as workers tended to Piscotty and a hush fell over the crowd.
"He could move the things he needed to move, so that was a relief," Matheny told MLB.com. "But it was, without question, very scary."
St. Louis third baseman Matt Carpenter watched with an anguished look on his face.
"I thought he was paralyzed," Carpenter said, according to MLB.com. "I immediately thought he had broken his neck. I had 100 scenarios running through my head, and none of them were good. You instantly are thinking of all the worst possible scenarios of what could be going on out there. It's just a horrible, horrible moment."
It was the opener of a pivotal three-game series between the top two teams in the NL Central. St. Louis won 3-0 to move four games in front of Pittsburgh and can clinch its third consecutive division crown with another victory Tuesday night.
Both teams have already locked up playoff berths.
The 24-year-old Piscotty has provided a major boost to the banged-up Cardinals since making his major league debut July 21. He is batting .310 with seven homers, 15 doubles and 39 RBI in 61 games.
In addition to Piscotty, the Cardinals have lost star catcher Yadier Molina and 14-game winner Carlos Martinez to injuries recently after ace pitcher Adam Wainwright, slugger Matt Holliday, first baseman Matt Adams and outfielder Randal Grichuk missed long stretches of the season with various ailments.
Wainwright has been sidelined since April but hopes to pitch out of the bullpen in the postseason.
St. Louis owns the best record in the majors at 99-58.
The Associated Press contributed to this report.