The 20-year-old Niemann entered the final round of the season opener with a two-stroke lead and Niemann held off challenges from Tom Hoge and Richy Werenski.

Niemann birdied the final three holes to finish at 21-under 259 at Old White TPC.

"I've been thinking about this my whole life since I started playing golf, so it's unbelievable," said Hoge. "I still can't realise what happened today. I just need to calm down a little bit and just celebrate.

"It's just crazy. I'm really happy for all the support, my family, my coach. It's just crazy."

Niemann grew up in Santiago, Chile, won a pair of junior world titles and was the No.1 ranked amateur in the world before turning pro in 2018.

He played his first full season on tour in 2019, finishing No. 67 in the FedEx Cup standings.

In 2017, Niemann tied for 29th as an amateur after receiving a sponsor's exemption at The Greenbrier. He improved to a tie for fifth in 2018. He shot 64 in the final round for the third straight year.

It marks the first year since 1931 that there has been more than one tour winner under 21. Matthew Wolff won the 3M Open in June at 20 years, two months.

Niemann is the first third-round leader to win at The Greenbrier since its debut in 2010.

Hoge shot 65 and finished second at 15 under. Werenski faded to a 69 and finished in a four-way tie for third at 14 under.

Matt Jones was the best of the Australian contingent, his final round four-under score placing him in joint 10th position nine shots behind Niemann.

Cameron Smith was next best, finishing in a tie for 24th 13 shots off the pace.

Australian Associated Press