KIAWAH ISLAND (South Carolina) • Weathering a riveting, roller-coaster test of nerves over five hours, Phil Mickelson, who will turn 51 next month, won the PGA Championship on Sunday to become the oldest golfer to win a Major.

The record was previously held by Julius Boros, who was 48 when he won the 1968 PGA Championship.

Mickelson shot six-under 282 for the tournament - he had a final round of one-over 73 - to finish two strokes ahead of the runners-up, fellow American Brooks Koepka (74) and South Africa's Louis Oosthuizen (73).

The six-time Major champion is the latest in a growing group of sports stars, like 43-year-old American football quarterback Tom Brady, who have defied traditional retirement ages for athletes, proving that championships can be won in careers that last into middle age.

"I hope that this inspires some to just put in that little extra work, because there's no reason why you can't accomplish your goals at an older age," Mickelson said. "It just takes a little more work."

One of the most popular golfers for three decades, the final scene of his Sunday triumph made it obvious that his appeal had not waned.

At the final hole, Mickelson was enveloped by hundreds of fans, who surged past security guards and the police to celebrate alongside him. He called the experience "slightly unnerving but exceptionally awesome", and said he would "cherish it for my entire life".

Mickelson's achievement could prove to be a bookend to three decades in golf's spotlight.

He did not break through the Major barrier until he was 33, when he claimed the 2004 Masters during his 13th year on tour, but two more Green Jackets soon followed, in 2006 and 2010, as well as a victory at the 2005 PGA Championship.

There have been frequent, dispiriting setbacks along the way, including six second-placed finishes at the US Open and before Sunday's victory at the treacherous Ocean Course at Kiawah Island, Mickelson had not won a Major since the 2013 British Open.

However, he has remained a fan favourite, in part because of a daring style of play and because of his Everyman physique, which stands in stark contrast to the fit, muscular bodies of the modern golfer.

Mickelson's caddie Tim revealed that his brother, known as "Lefty" for his left-handed swing even though he is naturally right-handed, had never doubted himself over the course of his PGA Tour career, and still had the hunger and desire to win that drives all great players.

"Certainly it's probably higher than when I started caddying for him (in 2017)," he said. "I think the best players in the world all have that, and Phil has just carried that on for 35 years."

Mickelson's manager Steve Loy also predicted there was much more to come as his client now "thinks he's 25-years-old again".

The ageless wonder himself aims to take that attitude into next month's US Open at Torrey Pines, California, where he has designs on completing a career Grand Slam. In the modern era, only five players have achieved the feat - record 18-time Major champion Jack Nicklaus, Tiger Woods, Ben Hogan, Gary Player and Gene Sarazen.

It was only a week ago that the US Golf Association granted him an exemption to the June 17-20 Major, for which he had not qualified.

Mickelson said: "I know I'm playing well and this could very well be my last really good opportunity to win a US Open, so I'm going to put everything I have into it.

"I do believe that if I stay sharp mentally I can play well at Torrey Pines. I'll take two weeks off before that and go out to Torrey and spend time on the greens and really try to be sharp for that week."

AGENCE FRANCE-PRESSE, REUTERS, NYTIMES