Kurt Kitayama let an all-star cast of contenders back into the tournament with a triple bogey, only to beat them all with a clutch birdie and the best lag putt of his life to win the Arnold Palmer Invitational.

With five players tied for the lead with only three holes left, Kitayama pulled ahead with a birdie on the par-3 17th hole for the lead. Then, his 50-foot putt on the last hole stopped millimetres from the cup.

The tap-in par for an even-par 72 was the easiest shot he had all day.

Rory McIlroy roared into the mix with four birdies in a five-hole stretch around the turn, only to miss a 10-foot birdie putt on the final hole for the lead.

He had a 70 and finished one shot behind. So did Harris English, who went bogey-free on the weekend at crusty, windy Bay Hill for a 70.

Defending champion Scottie Scheffler was a foot away from having a close look at birdie and a chance to take the lead. Instead, his ball spun back into the rough on the 18th and he finished with a bogey.

Jordan Spieth was among six players who had at least a share of the lead over the final two hours. He missed four straight putts inside eight feet from the 14th through the 17th and played his last five holes in three over.

Spieth (70), Scheffler (73), Patrick Cantlay (68) and Tyrrell Hatton (72) all finished two shots behind.

They all had a chance, mostly because of one swing. Kitayama had a two-shot lead when he hit a wild hook out-of-bounds on the ninth hole, leading to triple bogey.

These are the kind of players who kept beating Kitayama - Jon Rahm by one shot in Mexico, Xander Schauffele by one shot in the Scottish Open, McIlroy by one shot in the CJ Cup in South Carolina last year.

This time, the 30-year-old Californian who toiled around the world to earn a PGA Tour card had the final say.

Kitayama finished at nine-under 279 and earned $US3.6 million ($A5.33 million).

"It went south on 9," Kitayama said. "All of a sudden, I'm not leading any more. I just fought back hard, and I'm proud of myself for that."

Of the top seven players, all of them have either won majors or played in the Ryder Cup. The exception is Kitayama, who groomed himself for a moment like this with so many close calls against players with polished pedigrees.

Kitayama, who played at UNLV, didn't find much success on the Korn Ferry Tour and took his trade overseas to the Asian Tour and European tour, with stops along the way on the Sunshine Tour in South Africa and the Japan Golf Tour.

Now he's No.19 in the world, with a red cardigan sweater for winning at Arnie's place and a big feather in his cap for the players he had to beat.

He made it difficult on himself on the 18th, pulling his tee shot into dense rough, but recovered with aplomb to finally have a PGA Tour title to show for his toils.

Rahm, meanwhile, finished in a tie for 39th - his first time outside the top 10 since the Tour Championship last August. He still managed to stay at No.1 in the world.

Australian Jason Day continued his strong form to all but punch his ticket to the Masters with a tie for 10th at five under, just four strokes behind the winner, after closing with a 70.