Fifty-year-old Phil Mickelson will try to become golf's oldest major winner on Sunday by capturing the PGA Championship at windy Kiawah Island.
The American left-hander, seeking his sixth major title, owned a one-stroke lead over Brooks Koepka as the final round began on the formidable Ocean Course, the longest layout in major history at 7,876 yards.
Mickelson would erase the major age win mark set by American Julius Boros when he won the 1968 PGA Championship at age 48.
World number 115 Mickelson stood on seven-under par 209 through 54 holes with compatriot Koepka, a four-time major champion, one stroke adrift and South African Louis Oosthuizen third on 211.
Mickelson led by five at one stage Saturday before stumbling with a bogey and double bogey at the 12th and 13th holes, squandering his huge edge but staying on top after Koepka made a bogey on the final hole.
"I'm playing a lot better than the score is showing," Mickelson said. "And I think if I can just stay sharp tomorrow, I'll post a score that better reflects how I'm actually playing."
Koepka and Mickelson were set to tee off in the final pairing at 2:30 p.m. (1830 GMT).
It's the first time since the 1981 Masters with Jack Nicklaus and Tom Watson that the final group in a major has two players with at least four major triumphs, and the first time it happens at a PGA since 1974.
"I'm in the final group. That's what you want," said Koepka. "If I strike it anything like I did the last three days, I'll have a chance."
Mickelson is 3-for-5 in majors with 54-hole leads or shared leads, winning at the 2004 and 2006 Masters and 2005 PGA but sharing second at the 2006 and 2013 US Opens.
With 16 years since his PGA victory, Mickelson would own the longest gap between wins at the same major if he collects the Wanamaker Trophy and the top prize of $2.1 million (1.7 million euros).
"Lefty" will try to complete a career Grand Slam next month at Torrey Pines in his hometown of San Diego by winning the US Open, where he holds the record with six runner-up results.
Mickelson is the oldest 54-hole leader in PGA history, surpassing 47-year-old Gene Littler from 1977, and only the fourth 50-and-over player since 1934 to lead entering the final round at any major.
Mickelson's spectacular shotmaking in blustery conditions has sparked the biggest cheers from a crowd limited to 10,000 people by Covid-19 safety measures.
Koepka, fighting through pain to play after right knee surgery two months ago, could become the 20th player to win a fifth career major. He took the 2017 and 2018 US Opens and the 2018 and 2019 PGAs.
Koepka, who turned 31 earlier this month, has been in the top five on the leaderboard after 13 of the past 14 rounds at PGA Championships, an unprecedented feat for the event and one unseen at any major since Tony Jacklin from 1969-1973 at the British Open.
American Kevin Streelman was fourth on 212 with South Africans Branden Grace and Christiaan Bezuidenhout on 213 and reigning US Open champion Bryson DeChambeau on 214 with fellow American Gary Woodland, the 2019 US Open winner, and Chile's Joaquin Niemann.
If Niemann wins, the 22-year-old South American will become the youngest winner in PGA Championship history, eclipsing the mark set by Rory McIlroy at age 23 when he won the 2012 PGA at Kiawah Island.
McIlroy, who snapped an 18-month win drought two weeks ago, was 12 adrift after three rounds.
American Jordan Spieth, who would complete a career Grand Slam with a victory, entered the last round seven off the pace, needing to match the best final-day fightback in PGA history to win.