Brooks Koepka's rise through the ranks of golf has been so meteoric the new world No.2 hasn't even grasped that he is already one of the greats.

At the age of 28 he has the golf world at his feet.

"I've actually never thought about that; three majors at 28, it's a cool feeling," Koepka said after winning the PGA Championship on Sunday.

The big-hitting American fired a four-under-par 66 at Missouri's Bellerive Country Club to earn a 16-under total and a two-shot victory from 14-time major winner Tiger Woods (64), with Australian Adam Scott (67) third at 13 under.

It is the Koepka's third major title in 14 months and second this year, having successfully defended his breakthrough 2017 US Open victory at Shinnecock Hills in June.

The Florida native is now one of just 46 players in golf's history to have won three or more majors in their career.

He joins elite company in Woods, Gene Sarazen, Ben Hogan and Jack Nicklaus as the only players to win the US Open and US PGA in the same season.

He joins Jordan Spieth, Woods, Nicklaus and Tom Watson as the only players since World War II with three majors before turning 30.

The muscular Koepka is already in the frame for a future nomination to the golf Hall of Fame.

"I'm excited for the next few years," he said.

Although he owns a European Tour victory and four on its secondary circuit, Koepka has just one win on the US PGA Tour outside the majors.

He admits his power game is suited to golf's biggest stage and is already eyeing a shot at a Masters green jacket.

"I've won three of the last six I've played in, so I guess (my game) suits the majors," a tongue-in-cheek Koepka said.

"I just need to figure out Augusta; I haven't quite had the results there I've had elsewhere."

Queenslander Scott emerged as Koepka's biggest threat during a grandstand finale when he joined his final group partner in a share of the lead at the 13th.

But 2013 Masters winner Scott's charge fizzled when he missed a short birdie putt at the 17th, which would have cut Koepka's lead to just one.

Four-time PGA champion Woods mounted a vintage charge with his six-under-par 64 equalling the day's best score, which is his best final round at the majors.

Woods' 266 was also the lowest total of his major championship career.

Jason Day faded with a one-over 71 that dropped the 2015 PGA Championship winner to a share of 19th at seven under, while Cameron Smith's 66 gave him a share of 56th at one under.

Marc Leishman (71) was three shots back of Smith in a tie for 71st.