After finishing his five-under 65 to get to nine-under on Sunday, Burns was done in the clubhouse when, at one point, Scheffler was among five players tied at 10-under.

The gusty wind and a strange sequence changed all that. And Scheffler needed three clutch putts for a 72 just to get into the play-off matching 25-year-old standouts and close friends.

"We're probably best friends. But at the same time I can assure you, he wanted to beat me more than anybody else and I wanted to beat him more than anybody else, and it just happened to be the two of us at the end," Burns said of Scheffler.

"It's going to be a fun story that we'll get to have for the rest of our careers, and fortunately I got the better end of it this time, but hopefully we're at the beginning of these situations in the future."

Burns' seven-stroke comeback matched Nick Price in 1994 for the biggest in a final round to win the $US1,512,000 ($A2.1m) Charles Schwab Challenge.

"We're probably best friends. But at the same time I can assure you, he wanted to beat me more than anybody else and I wanted to beat him more than anybody else." - Sam Burns.

Australia's Cam Davis (72) finished in a tie for seventh at five-under, Matt Jones (69) was a shot further back, and Lucas Herbert (72) ended three-over.

The playoff began with Burns and Scheffler driving into the fairway at No.18, the same hole where just moments earlier Scheffler made a six-foot par after his approach on his 72nd hole went into the bunker.

Scheffler got on the green with his approach in the play-off, but was 36 feet away. Burns hit just off the back edge of the green and used his putter, with the ball curling the last few feet into the cup. Scheffler made a good run with his putt, but didn't have a birdie all day.

"Pretty straightforward putt. A little downhill, breaking left to right the whole way, played it about a foot out and just tried to match the speed up," Burns said of the play-off deciding putt. "I honestly thought it was going to be a little bit short when I hit it, and that's kind of why my reaction was what it was. I thought I left it short.

"I mean, to see that go in, that was obviously really cool."

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It was the third win this season for Burns, and his fourth overall in his last 27 starts. The world's 10th-ranked player won at Valspar for the second time in March.

Masters champion Scheffler was going for his fifth victory in his last 10 starts. He missed becoming the first player since Tom Watson in 1980 with five wins in a PGA Tour season before the start of June.

Brendon Todd (71), who played in the final group with Scheffler, gave up his share of the lead with back-to-back bogeys at 11 and 12. That dropped him to eight-under, where he stayed to finish in third alone. That was a stroke ahead of Tony Finau (67), Davis Riley (69) and Scott Stallings (72).