Hernandez extended his glove over the center-field wall to catch a ball hit 395 feet, according to Statcast™, to deny Tommy Pham of a home run during the first inning.
Hernandez knew he had a chance on Pham's ball off the bat.
"When I saw the ball, I tried to see how far [it was] between me and the wall," Hernandez said. "I said I had a chance to grab that ball. … I had a good jump, and I grabbed it."
But Hernandez's defensive showing didn't stop there. He made a sliding catch at the right-center-field wall to end the seventh inning -- with the bases loaded - and he turned in another running slide for a catch on the warning track during the ninth.
"That's one of the best defensive games I've seen one player have with all the plays he made," Giants manager Bruce Bochy said. "He's a gifted outfielder. It's exciting to watch those kind of plays."
Hernandez's impact wasn't lost on Cardinals manager Mike Matheny, who is familiar with AT&T Park from his days in a Giants uniform.
"Their center fielder probably took away three or four runs today," Matheny said. "That's one of the best catches we've seen this year, only because of the speed where he got to the wall."
Pham, an outfielder himself, was equally impressed.
"He was playing me in right-center, and he went all the way to left-center and caught that. Just a great catch [by] him," Pham said. "Am I surprised he caught it? Not really, because I know he's a great center fielder, and he covers ground."
Hernandez's effort on the field Sunday matched his recent tear at the plate. He's hit .306 over his past 59 games.
"It's part of my job -- try to hold the team on defense," Hernandez said. "And recognizing that ball [in the first], try to jump at the wall. The good thing is that I catch it."
Jonathan Hawthorne is a reporter for MLB.com based in the Bay Area. This story was not subject to the approval of Major League Baseball or its clubs.