American David Kocher captured his biggest victory as a pro on Sunday, beating Japan's Yuwa Kosaihira in a playoff at the weather-affected Haikou Championship in Haikou, Hainan province, the third event of this year's PGA Tour Series-China.

After extended weather delays on Saturday, the third round resumed at 7:20 am on Sunday in a bid to finish the tournament before anticipated lightning in the afternoon.

Kocher and Kosaihira both carded 6-under 66s over the final 18 holes at Sunac Haikou 3KM Golf Club, but it was Kosaihira who had the first shot at winning it outright.

After Kocher grabbed the early clubhouse lead at 10-under, Kosaihira hit the flagstick with his approach on the 18th but couldn't drain a 15-foot putt to take the lead.

After the final groups failed to match the clubhouse leaders, Kocher and Kosaihira headed to a playoff, which landed comfortably in Kocher's lap after Kosaihira lost his ball after ricocheting it off a cart path and into the bushes.

He went on to make a double bogey while Kocher sunk his 10-foot birdie putt to seal the victory.

Kocher, who turned 23 on Saturday, was thrilled with the manner of his victory.

"This is definitely the biggest win of my career, and it feels the best," he said.

"I'm really happy with where my game is. I've been playing well this whole year, so it's definitely a big confidence boost.

"I'll celebrate a little bit tonight and then have an early flight home (to the US) in the morning and then celebrate with friends and family there."

After starting the final round with eight straight pars, Kocher picked up his first birdie on the ninth hole, sparking a flawless back nine that saw him reel off five more sub-par holes en route to a bogey-free round.

It was a sensational performance by Kocher, who only earned conditional status at Q-school in February.

At the PGA Tour Series-China's season-opening event in Chongqing, he progressed through a Monday qualifier and finished third before another top-20 finish two weeks ago in Sanya helped him earn his spot in Haikou.

"No more Monday qualifiers. That's a huge plus. I can book my trips and not have to worry about coming out early for Mondays, so it's a great positive," Kocher said.

"It feels awesome. My goal for this year was just to finish in the top 25 and get to the second stage (of the Web.com Tour final qualifying tournament), so I think this win will give me a huge boost.

"I can set some new goals for myself."

Kocher was a highly successful amateur, winning the North Carolina Open in 2016 and 2017 while still attending the University of Maryland.

He won again on the GPro Tour at Mimosa Hills Country Club after he graduated in 2018, but he said those triumphs paled in comparison to winning at Haikou.

Singapore's Quincy Quek, who was playing in the final group, came up one shot short of a playoff after carding a 68 to finish solo third, one stroke ahead of former PGA Tour player Justin Hicks, who finished strong with a tournament-low 7-under 65.

Australia's James Marchesani shot a 72 to finish fifth at 7-under, one ahead of three players in a tie for sixth.

China's Zheng Ouyang started the final round with a one-shot lead but dropped to a tie for 10th after a finalround 76.

Despite no player managing to go bogey-free in the opening three rounds, 10 players were bogey-free over the last 18 holes: Lloyd Jefferson Go, Trevor Sluman, Bryden Macpherson, Douglas Quinones, Jin Cheng, Kevin Yuan, Luke Kwon, Wenyi Huang, Kevin Lee and Chen Zihao.

Sluman, who won the Sanya Championship, shot 73-69-73-69 to finish 4-under, good for a tie for 10th.