"Winning is hard. It's really, really hard," said two-time major winner Thomas on the 18th green as he stood next to wife Jill and 5-month-old daughter Molly.
"I've worked my butt off and stayed patient, stayed positive."
Thomas played bogey-free in dry, fast conditions at Harbour Town for a three-under 68, making a 25-foot birdie putt on the 16th that looked like it might be the winner until Novak matched him with a big birdie of his own for a 68.
Novak, who has had three good chances to win in his last 14 tournaments, had an eight-foot birdie putt on the 18th hole in regulation that was left all the way.
In the playoff, Novak missed from just inside 35 feet, setting the stage for Thomas. The putt was so pure that Thomas dropped his putter before the ball dropped, stooping over and clutching both arms to celebrate a win that felt long overdue.
His previous win was the PGA Championship at Southern Hills in May of 2022. His game slipped and he missed the FedEx Cup playoffs for the first time in 2023, and he was left off the Presidents Cup team a year ago.
His game was back in order — he cracked the top 10 again — and needed only a victory to confirm his game was back among the elite.
"I didn't realise how much I missed winning," Thomas said.
Thomas and Novak finished at 17-under 267, three shots clear of Daniel Berger (65), Mackenzie Hughes (67) Brian Harman (69) and Maverick McNealy (70).
After missing five straight cuts, Australian Cam Davis birdied three of his last six holes to tie for 13th at 10 under to pick up $US364,000 ($A570,000) at the $US20 million Signature event.
But Davis will curse dropping four shots in four holes mid round en route to a Sunday even-par 71.
Fellow Australians Adam Scott and Jason Day shot matching 73s and fell into the tie for 54th at four under along with Karl Vilips (74) while Min Woo Lee (68) was a shot further back..
Thomas won for the 16th time on the PGA Tour, and to his recollection, he has never had to make a putt of length on the 18th hole to win by a shot.
"That was as fun as I thought it would be," Thomas said.
Thomas and Novak pulled away in the middle of the round from a tight leaderboard — a four-way tie at one point as they were joined by 54-hole leader Si Woo Kim and McNealy.
Defending champion Scottie Scheffler even got in on the act, just briefly. He had pulled within two shots when he took on a high-risk shot needing eagle to have a legitimate chance.
That found the water, leading to double bogey. He still shot 70 and tied for eighth, his third straight top 10 while contending into the final hour.
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