But Koepka said his surgically repaired knee hurt too badly after the wild scene on the 18th hole.
The four-time major champion suggested that a fan may have hit his right kneeon purpose as both players were caught up in a swarm of people who pushed past the ropes to circle the green.
Even if the blows to his knee were unintentional, Koepka said the celebration was troubling.
"Yeah, it's cool for Phil," Koepka said. "But getting dinged a few times isn't exactly my idea of fun."
Fans flooding the 18th fairway is a familiar custom at the British Open. It also occurred at East Lake in 2018 as Tiger Woods finished off his victory at the Tour Championship.
"I've never had something like that," said Mickelson, the 2013 British Open champion. "It was a little bit unnerving, but it was exceptionally awesome, too."
Koepka was unsure if he re-injured the knee, only that it hurt badly after he came through the crowd. He planned to ice it.
Koepka had scheduled a few weeks off before playing in the US Open at Torrey Pines next month.
PGA Championship officials did not immediately respond to a request for comment about the crowds.
Brooks Koepka (right) suggested a fan at the PGA Championship may have hurt his injured knee on purpose. Photos / AP
Fans, limited by organisers to about 10,000 a day because of Covid-19, had followed the 50-year-old Mickelson throughout the tournament and excitement grew steadily as he was set to make history as the oldest to win a major championship.
Mickelson drove his tee shot on the final hole to the left, into fans along the ropes. After Mickelson's approach landed safely on the green, fans pushed past marshals and security to flood the fairway.
People quickly swarmed over both competitors and their caddies. Mickelson, who had his arm around a sheriff's deputy at one point as he walked through, and Koepka appeared to emerge unscathed.
Koepka said he was trying to protect his knee as he moved through the scrum. He had surgery in March for a dislocated knee cap and ligament damage.
"I don't think anybody really understands until you're coming out of surgery," Koepka said. "I mean, even when I was doing rehab and there's five people kind of standing by your knee, you get a little skittish."
Koepka wondered if someone purposely tried to hurt him. "I don't know, it felt somebody tried to ..." he said, cutting off his thought. "I don't know what the deal was, but it's what it is."
Mickelson had his own odd moments with the gallery this week. On Saturday, he hit a ball on the 16th hole that landed near a cart tire on the right.
Mickelson had to tell one fan, "Don't touch me," and left a bit rattled by the encounter.
On Sunday, it was different vibe as Mickelson smiled his way through people as he moved to the green, where he was putts away from his sixth career major title.
Tim Mickelson, Phil's younger brother and caddie, remembered how Woods just stayed ahead of the fans on his march toward the green at East Lake three years ago.
Tim Mickelson said he wasn't nervous inside the throng.
"It was, obviously, a cool sight," he said. "Considering where we are in the world right now, it was sort of weird."
