The PGA of America has apologised after fans surrounded Phil Mickelson and Brooks Koepka on the final hole of the US PGA Championship at Kiawah Island.

Despite the Covid-19 pandemic, spectators swamped the American pair on the way to the 18th green and winner Mickelson, 50, said it was "unnerving".

Koepka recently had knee surgery and said he "got dinged a few times in the knee in that crowd".

PGA of America chief executive Seth Waugh has

apologised to both players.

Mickelson's victory meant he became the oldest man to win a major title, with Koepka finishing in joint second place.

The US PGA Championship's Covid-19 protocols for fans included "no handshakes, fist bumps, autographs, photographs or selfies"; for people attending to "respect their [players'] space and watch your distance" and "avoid unnecessary touchpoints and large crowds". Fans who had not been vaccinated were advised to wear masks when they could not be socially distant.

But Mickelson needed a security and police escort to make his way through the jam-packed crowd of spectators to complete his historic moment.

"While we welcome enthusiastic fan engagement, we regret that a moment of high elation and pent-up emotion by spectators... briefly overwhelmed security and made two players and their caddies feel vulnerable," said Waugh.

"We always put player safety at the top of our list and are grateful order was restored."

Meanwhile, Mickelson said he had been inspired by Tampa Bay Buccaneers quarterback Tom Brady.

Brady, 43, won a seventh Super Bowl when he led the Bucs to victory in February and played with Mickelson in a charity golf match against Tiger Woods and Peyton Manning in Florida last year to raise money for COVID-19 relief efforts.

"He's [Brady] actually a big motivation, because of how hard he works to be the best and to elongate his career," said six-time major winner Mickelson.

"There's no reason why at an older age, you cannot be at your best.

"It just takes a little more work. I wasn't getting the results - but I believed it, and I had people believe in me."