MEMPHIS, Tenn. — Justin Thomas won the FedEx St. Jude Invitational on Sunday to take the No. 1 spot in the world for the first time since June 2018.

Thomas dueled defending champion Brooks Koepka down the final holes, sealing the World Golf Championship victory on the par-5 16th. Thomas took the lead for good with his second straight birdie, while Koepka bogeyed.

Koepka pulled within a stroke with a 39-footer for birdie on No. 17. But Koepka put his tee shot into the water along the 18th fairway on his way to double bogey, allowing Thomas to finish up an easy par putt for what wound up a three-stroke victory.

Thomas closed with a 5-under 66 to finish at 13-under 267 and take the $10.5 million winner’s check for his 13th PGA Tour title. At 27, he became the third-youngest player since 1960 to reach 13 PGA Tour wins, trailing only Tiger Woods and Jack Nicklaus.

This was the fifth time Thomas rallied to win, and he matched his biggest comeback after starting the day four strokes back of third-round leader Brendon Todd. Thomas has three wins this season, two since the start of the year.

The last time Thomas was No. 1, he spent four weeks at the top of the ranking. He will supplant Jon Rahm, who became No. 1 after winning at Memorial two weeks ago.

Koepka will go to TPC Harding Park in San Francisco looking to defend his PGA championship title. He finished with a 69 and tied for second with Phil Mickelson (67), Daniel Berger (65) and Tom Lewis (66).