Whiteside took a throw from left fielder Cody Ross and held on during a collision at the plate with Fielder, allowing the Giants to preserve a 5-4 victory over the Brewers.
"I knew he was on second base, I knew they were going to send him and I knew what he was going to try to do," said Whiteside, starting in place of Buster Posey, who was injured Wednesday night in a collision at the plate. "Cody made a perfect throw, a one-hop throw. I was able to back up and catch it on a big hop and prepared myself."
Fielder pushed his arms at Whiteside, who pushed back and held on to the ball for the final out in the eighth.
"If he's coming at you, you can go at him a little bit," said Whiteside, who flipped the ball to home-plate umpire Mike Muchlinski after the collision. "There's no rule in the book says you can't take it to him a little bit, you know?
"That's what you can do if you get the ball in time," he said. "Cody made a perfect throw. It allowed me to do that."
The play came just two nights after the Marlins' Scott Cousins barreled into Posey, breaking the star catcher's left leg and tearing ligaments in his left ankle.
"I had a few flashbacks," Ross said of the Posey play. "[Whiteside] had it perfect on his side, so he could maneuver any way he wanted to. I'm glad he got him out and everybody survived."
Giants manager Bruce Bochy said the play Friday night was a different situation than the collision involving Posey.
"He had the ball, so he could set up a little bit," Bochy said. "The catcher's got a better chance than when he's trying to catch a ball. That's when he's really vulnerable. Still, that's a big guy bearing down, and Whitey did a great job, as Cody did."
Fielder gave Whiteside credit.
"It was a good play," he said. "He saved the game."
Joe DiGiovanni is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.