Justin Thomas regained the World Number One spot after seeing off defending champion Brooks Koepka in a thrilling final round battle to win the WGC-FedEx St Jude Invitational title for the second time in three years.
Thomas, who won this event when it was held at Firestone Country Club in 2018, shot a final round 65 to come from way back to secure a three shot victory, but it was not all plain sailing on a topsy turvy afternoon in Memphis.
The 27-year-old began the day four shots behind overnight leader Brendon Todd but he had climbed to the top of the leaderboard by the time the final pairing had reached the turn after making four birdies on his front nine.
Thomas fell back into a five way tie for first place when he dropped his only shot of the day at the 12th and he could do nothing to prevent Koepka from taking the outright lead when the four time Major Champion rolled in from ten feet on the 13th.
After making back to back pars, Thomas enjoyed a huge slice of luck when his tee shot at the 15th took a favourable bounce on the cart path and made its way through some trees before landing in a nice spot 52 yards from the hole.
He made an unlikely birdie there before picking up another shot at the long 16th despite getting into tree trouble.
Thomas looked to be home and dry after Koepka, who was playing in the group behind him, made a bogey on the 16th but the defending champion bounced back with a magnificent birdie putt from 40 feet on the 17th to reduce the gap to one as Thomas parred his way home.
But any nerves Thomas may have had were alleviated when Koepka put his tee shot at the 18th in the water before eventually carding a double bogey to finish three shots behind the champion, whose last stint at the top of the Official World Golf Ranking came in 2018.
After clinching his second World Golf Championships crown, Thomas said: "It was a hard fought day, but it meant a lot how we did it, being four behind to start the day.
"I haven't exactly played well coming from behind in the past and I feel like I learned a lot from that.
"Right now I'm obviously very happy and elated that we got it done today but I need to work on some things and get ready for the PGA next week and try to win another Major."
Thomas is hoping to keep hold of the World Number One spot for longer than he did last time, when he stayed at the summit for four weeks.
He said: "I feel like I'm a better player and I feel like I'm more complete of a golfer now than I was then."
Koepka finished in a tie for second on ten under alongside Americans Phil Mickelson and Daniel Berger and Englishman Tom Lewis, who followed up his course record equalling 61 on Saturday with a 66 at TPC Southwind on Sunday.
Shane Lowry, Matthew Fitzpatrick and Louis Oosthuizen were in the large group another stroke further back alongside Xander Schauffele, Jason Day and Chez Reavie.
Thomas got his first birdie of the day at the second after playing a top quality iron shot to six feet and tapping in to move to nine under par.
He then got up and down from the left rough for a birdie at the third to make it two in a row before safely parring his next three holes.
Thomas slotted in another birdie from 15 feet at the seventh before joining Todd at the summit on 12 under with a fine 20 footer on the ninth green.
And when Todd, who had missed a number of birdie efforts in the early stages of his fourth round, could not convert his short par putt at the eighth, Thomas was the new outright leader.
Thomas created another birdie chance at the tenth but his 12 foot try slid just by.
But when he made a bogey at the 12th, Thomas found himself tied with Berger, Koepka, Todd and Lewis on 11 under as the tournament was flung wide open.
Koepka, whose last victory came at this event last year, birdied the 13th to take over at the top of the leaderboard but Thomas made a six foot birdie at the 15th to join him on 12 under after getting lucky with an errant tee shot.
Thomas rode his luck again at the 16th as he got into tree trouble before playing two brilliant recovery shots on his way to making another birdie and regaining the outright lead.
Koepka gave Thomas breathing space at the top when he bogeyed the long 16th but as Thomas made pars at the final two holes, Koepka got a birdie on the 17th to pile on the pressure.
But when Koepka's tee shot at the last landed in the water, Thomas could celebrate a hard fought victory and his return to World Number One.
Koepka, who has struggled with a knee injury since winning here last year, is pleased the with shape his game is in heading into next week's US PGA Championship, where he is the double defending champion.
He said: "I feel good.
"This is where we wanted to be, peaking for the PGA. I feel like my game's right there, everything's solid.
"I hit a lot of good putts today, just didn't go in. Yeah, I mean, I'm pleased with it."
