Despite seeing his four-shot overnight lead wiped out early in the final round, the 29-year-old American's level-par 71 was enough to hold off the challenge of Finland's Sami Valimaki, who hit a closing 69 to finish two shots back.

Knapp saw his four-shot buffer halved as he bogeyed two of the first three holes, Valimaki moving within one with a birdie on the fourth.

The Finn eagled the short par four seventh to draw level as Knapp claimed his first birdie of the day.

He added just one more on the 14th, but Valimaki had dropped three shots by then and could not close the gap again.

Scotland's Robert MacIntyre finished six shots back in a tie for sixth after a closing 69, but England's Matt Wallace – who shared the halfway lead – slipped to tied 33rd with a 74.

Knapp's win earns him a place at the US Masters, PGA Championship and the five signature events remaining on the PGA Tour.

"Didn't necessarily have my best stuff today, that's for sure," Knapp said.

"Knew it was going to be nerve-wracking. Knew it was going to be tough. But I was super pumped on how I played the finishing stretch.

"They needed a security guy and I was like, 'I don't know if I'm big enough, but I can stand there and look tough'."