Brooks Koepka outdueled Viktor Hovland and Scottie Scheffler in a back-nine battle Sunday to win the PGA Championship for his fifth major title, giving Saudi-backed LIV Golf a milestone major triumph.

The 33-year-old American captured his third PGA Championship and became the first player to win a major since joining LIV, firing a three-under par 67 to finish 72 holes at Oak Hill on nine-under 271.

"It's incredible," said Koepka, only the 20th player to win five or more majors. "I'm not sure I even dreamed when I was a kid I would win this many."

Norway's 11th-ranked Hovland, chasing his first major title, and American Scheffler, last year's Masters winner and the new world number one, shared second on 273.

"I put up a good fight. I played great today," Scheffler said. "I gave the guys on top of the leaderboard something to think about and I made a little bit much a move.

"But Brooks just played some fantastic golf this week. He played too good this weekend for me to catch up to him."

There were a smattering of boos for Koepka as he walked onto the 18th green to make the concluding putts for the title, a sign of the bitter acrimony that has engulfed golf since the launch of the LIV circuit last year.

But Koepka calmly finished off an impressive romp, his first major win since 2021 knee surgery sidelined him for most of the past two seasons.

"I look back at where we were two years ago," Koepka said. "I'm so happy right now. I'm at a loss for words. But this is the coolest thing."

Australia's Cam Davis and American Kurt Kitayama shared fourth on 277 with another LIV player, American Bryson DeChambeau.

Four-time major winner Rory McIlroy shared seventh on 278 with Austrian Sepp Straka.

Koepka was among the stars who jumped from the PGA Tour to breakaway LIV Golf, which offered record US$25 million purses for 54-hole events, despite concern over Saudi Arabia's human rights record.

The PGA banned LIV talent from its events, with a legal fight between them due in court next May. In the meantime, the majors have provided the only outlet for competition between players from the rival tours.

In all, there were six major winners from LIV in the field of 156 with a combined 15 major crowns, none of them won since joining the upstart circuit, including Australian Cam Smith's British Open title last July.

Koepka led entering the final round at last month's Masters but, in his words, "choked" away the green jacket to Spain's Jon Rahm.

After sharing second at Augusta National with LIV's Phil Mickelson, Koepka's three PGA wins puts him behind only Tiger Woods, Jack Nicklaus and Walter Hagen.

In the closing drama, Hovland sank a birdie putt from just inside eight feet at 14 but Koepka matched him from just inside four feet to reach nine-under and stay one ahead of the 11th-ranked Norwegian with Scheffler three back.

Hovland was undone by a 9-iron shot from a fairway bunker at 16, where he embedded his ball into the bunker wall and went on to make double bogey.

Koepka sank a birdie putt at 16 from just inside five feet to reach 10-under and lead by four.

"I thought I handled myself pretty well," Hovland said. "Pretty unfortunate on 16 but I don't feel like I gave it away.

"Brooks deserved to win. He hit a lot of great putts and a lot of great shots."

Scheffler birdied 18 from just inside 16 feet and Koepka took bogey at 17 after finding the right rough off the tee, sending Koepka to the final hole two up on the American.

Koepka dropped his approach inside 10 feet and two-putted for victory.

World number three McIlroy from Northern Ireland was trying to win his first major title since 2014.

McIlroy's playing partner, US club professional Michael Block, aced the 151-yard par-3 15th on the fly with a 7-iron and was cheered all the way along his walk to the hole. It was the first hole-in-one by a club pro in the PGA since 1999.

Block shot 71 to share 15th on 281, earning a spot in next year's PGA field. (AFP)