World No.1 Brooks Koepka birdied three of the first six holes on the way to winning his first career WGC title Sunday at the St. Jude Invitational.

Koepka outclassed third-ranked Rory McIlroy in a last-duo duel of four-time major champions, their first-ever pairing in a final round, for the victory at TPC Southwind in Memphis, Tennessee.

"It's so special. It gives me chills thinking of it," Koepka said. "It's one of my favorite stops on the tour and to win here is very special for me."

Koepka, who defended a major title at this year's PGA Championship, fired a bogey-free five-under-par 65 to finish on 16-under 264 after 72 holes and defeat American Webb Simpson by three strokes.

It was the seventh career US PGA title for Koepka, the 2017 and 2018 US Open champion and 2018 and 2019 PGA Championship winner. His other prior US tour wins came in 2015 at Phoenix and in last year's CJ Cup in South Korea.

"I've been playing so well as of late," Koepka said. "Everything comes if you wait. If you keep playing well and putting yourself in contention good things will happen."

The final round brought only more frustration for McIlroy, who missed the cut at the British Open in Portrush, Northern Ireland, but had taken a one-stroke lead after firing a 62 on Saturday.

Koepka praised the tournament's charity, the St. Jude Children's Hospital in Memphis, saying it put the highs and lows in golf into a greater perspective.

"I've taken a trip to the hospital. It changed my life," he said. "It puts everything in perspective, how little golf means, how much life matters."

Simpson was second on 267 after a closing 64 with Australia's Marc Leishman third on 268 and McIlroy sharing fourth on 269 with England's Tommy Fleetwood and Matthew Fitzpatrick. Spain's Jon Rahm was seventh on 270 with England's Ian Poulter another stroke adrift.