Westwood, who led DeChambeau by one after round three, dropped two shots on the front nine and another at the 14th in a 73 that saw him finish 10 under. Canadian Corey Conners finished third, a further two shots behind .
DeChambeau revealed that he had received a text from 15-time major winner Tiger Woods prior to the start of the final rounds. Woods is recovering in hospital following a car crash and DeChambeau said: “We talked about just keep fighting, no matter what happens, and play boldly like Mr Palmer said.”
DeChambeau added: “It’s beyond my wildest dreams to win Mr Palmer’s event. I came here as an amateur, he gave me an invitation, and I loved this golf course the minute I arrived. I love the atmosphere and I love the fans. I loved what Mr Palmer did with this place and what he’s done and his legacy he’s left here. It’s quite amazing.”
DeChambeau dropped a shot at the opening hole of his final round, but Westwood bogeyed the third following a wild tee shot which was close to going out of bounds. It left Westwood and Conners contesting the lead, but they were soon joined by DeChambeau, who holed from 35 feet to birdie the fourth and join the leaders.
There was soon a four-way tie at the top when former Open winner Jordan Spieth birdied the fourth and sixth to reach 10 under.
However, DeChambeau and Westwood both birdied the 565-yard par-five sixth in wildly contrasting fashion. DeChambeau again took on the 300-yard carry over a lake, smashing a 377-yard drive into a fairway bunker, just 88 yards short of the green. He was wayward with his shot from the sand but produced a superb chip to four feet and holed the putt. Westwood’s tee shot was more conventional, following the fairway round the water, and left him with 256 yards to the hole. He missed the green in a similar place to DeChambeau but Westwood got up and down for birdie.
The Englishman bogeyed the next and with Spieth and Conners also dropping shots, DeChambeau enjoyed the outright lead on 11 under. A birdie from Westwood from 28 feet at the par-five 12th took him back into a share of the lead, but he bogeyed the 14th and from then, DeChambeau maintained his advantage.
He had a scare at the 18th when his birdie attempt rolled almost six feet past the hole but he held his nerve to seal a hard-fought win.
“I thought we had a really good battle,” said Westwood. “It was never really more than a one shot difference all day. There were tough conditions out there. It was a day for playing sensible and hanging on and grinding out the pars.”
Rory McIlroy’s challenge evaporated as two tee shots into the water saw him double bogeying the sixth on the way to a 76 which left him in a share on 10th place on three under.
Bryson DeChambeau’s winning gear
Driver: Cobra LTD Pro (7.5°)
Fairway Woods: Cobra King Prototype B 3 (10.5 and 13.5)
Irons: Cobra King Prototype Utility (4, 5), Cobra King Forged Tour One Length (6-PW)
Wedges: Artisan Prototype (47, 52, 58)
Putter: SIK Pro C-Series Armlock
Ball: Bridgestone Tour B X