DeChambeau holed a 40-foot birdie putt on the front nine and a 50-foot par putt early on the back nine.

He closed it out with a nervy five-foot par putt for a one-under 71 that gave him an 11-under 277 total and a one-shot victory over the 47-year-old Westwood.

DeChambeau's round matched the low score of the day, one of only three under par in the toughest final round at Bay Hill in 41 years.

DeChambeau and Westwood were never separated by more than one shot over the final 15 holes, a fascinating duel of generations that came down to the last shot.

After Westwood's drive on 18 had stopped in a divot, he managed to find the green and two-putt for a par from 65-feet.

DeChambeau's birdie effort on the closing hole slid by the hole and after regathering himself he sunk the pressure-packed winning putt.

Westwood closed with a 73, not a bad score considering the average of 75.49 was the highest for a final round since 1980.

"I don't even know what to say, to win at Mr Palmer's event, it's going to make me cry. It means the world to me." – Bryson DeChambeau

"I really enjoyed myself. You don't get the opportunity to have a proper battle on a good golf course, with a good player, in tough conditions that often for a big title," Westwood told Sky Sports.

Corey Conners holed a 15-foot eagle putt on the 16th to get within one shot of the lead but ultimately had to be content with third at eight-under after a 74.

Jordan Spieth took bogey on three of his last four holes for a 75, dropping him into a three-way tie for fourth with Andrew Putnam (71) and Ricky Werenski (73).

Queensland's Jason Day never got it going after starting Sunday five shots off the pace, failing to make a birdie in a seven-over 77 to finish in a share of 31st.

DeChambeau rose to No.6 in the world with his ninth PGA Tour victory, and he became the first player this season with multiple victories, to go along with his US Open title in September.

"It's been quite a battle," DeChambeau said in a television interview on the 18th green.

"I don't even know what to say, to win at Mr Palmer's event, it's going to make me cry.

"It means the world to me.

"I got a text from Tiger (Woods) this morning and he obviously had done really well here and we talked about just keep fighting no matter what happens and play boldly like Mr Palmer said."