BOSTON (AFP) - Justin Thomas fired a final round five-under 66 to win his fifth tournament of 2017, outduelling fellow American Jordan Spieth on the back nine at the Dell Championship on Monday.
The two Americans battled hard down the stretch until Spieth saw his hopes dashed on the fairway at the 18th when his approach sailed right and landed in a large bunker. His next shot travelled clear across the green as he finished with a bogey six on the hole.
Thomas completed the second tournament of the PGA Tour playoffs with a 17-under 267 total for a three-shot victory which propelled him into second place in the FedExCup standings behind Spieth.
"I have had a great year, just two more events to finish it off," said Thomas.
Spieth's bungle on the 18th allowed Thomas, who was in the group behind, the luxury of taking a victory stroll up the same fairway which he easily parred.
Spieth's self-destruction at the Dell came one week after he blew a five-stroke lead in the final round and lost to Dustin Johnson in a playoff at The Northern Trust to open the post-season.
Spieth, who shot a 67, finished solo runner-up at 14-under 270 while Australian Marc Leishman fired a 70 to place alone in third, four strokes back of Thomas.
Spain's John Rahm (68) and England's Paul Casey (70) tied for fourth at 12-under 272 at the par-71 TPC Boston.
Thomas, who won the PGA Championship last month, erased a two-shot deficit over the final nine holes for his Tour-leading fifth win of the season. He bogeyed No. 11 but closed with a pair of birdies and five pars to pull away from Spieth.
"Yeah, it was a good day. It was a patient day," said Thomas. "It just was a great week because I felt like I didn't have my best stuff at the start of the week and that's just something I've gotten so much better at, and I'm proud of myself more than anything."
Spieth had a bogey at the 12th and a birdie at No. 13 before making bogey at Nos. 14 and 18. He got off to a strong start with three birdies and an eagle over the first four holes.
"I've been striking the ball well. I didn't think anything was going wrong," he said. "I got unlucky on No. 12, and from there, the one on No. 14 was just a bad swing, and that one really hurt. I brought it back on No. 13. Fourteen was the difference-maker for me."
Leishman saw the lead disappear with five bogeys on the back side, including three straight beginning at No. 10.
"I got things going just the way I wanted to on the front and then a bad tee shot on No. 10. There was some tough holes out there," he said.
Kevin Na (66), Patrick Reed (66), Pat Perez (67) shared sixth place with Phil Mickelson, who shot 68.
World No. 1 Johnson stumbled to a 73 and finished in a tie for 18th.
The top 70 players on the playoff points list now advance to the BMW Championship, set for Sept 14-17 at Conway Farms Golf Club in Illinois.
Then the top 30 players following the BMW Championship will qualify for the Tour Championship at East Lake Golf Club in Atlanta, beginning Sept 21.