"I hope so," Thomas said Sunday after winning the WGC-FedEx St.Jude Invitational to take the top spot for the first time since June 2018.

"I feel like I'm a better player, and I feel like I'm more complete of a golfer now than I was then."

Thomas duelled with defending champion Brooks Koepka down the final holes but proved the more steady in the closing stages to win by three strokes.

Thomas closed with a five-under 66 at TPC Southwind to finish at 13-under 267 and seal his 13th PGA Tour title.

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At 27, he became the third-youngest player since 1960 to win 13 PGA Tour events, trailing only Tiger Woods and Jack Nicklaus.

"I've been fortunate to have a good career so far but I plan on playing out here for a long time and have a lot of things that I still want to accomplish," Thomas said.

RIGHT: Jason Day has now posted three consecutive top-10 finishes. PHOTO: Stacy Revere/Getty Images.

One sign of Thomas' growth was this was the fifth time he 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 the Memorial two weeks ago and tied for 52nd in Memphis.

Koepka will go to TPC Harding Park in San Francisco looking to defend his US PGA Championship title.

He finished with a 69 and tied for second with Phil Mickelson (67), Daniel Berger (65) and Briton Tom Lewis (66) at 10-under par.

Queenslander Jason Day (67) was within a shot of the lead late on Sunday but a bogey on his final hole left him at nine-under and a share of sixth.

Day – the 2015 US PGA Championship winner – has had three top-10 finishes in a row as his focus shifts to the first major of 2020.

Overnight leader Todd, aiming for a third win this season, faded with a 75 in the final round to slide to tied-15th.