The 635th-ranked New Zealander Ben Campbell beat "frustrated" major winner Cameron Smith by one stroke for a stunning triumph at the $2 million Hong Kong Open on Sunday.

Campbell roared to his first title on the Asian Tour with back-to-back birdies on the last two holes to card a final-round four-under-par 66 at a sunny Fanling.

The unheralded Kiwi finished on 19-under overall to snatch a famous victory in the LIV-supported International Series event.

"I was battling all day," said Campbell, whose career has been stymied by injuries.

"I've had quite a few injuries and bulged discs in the back and things like that, so I had to change the swing quite a bit, especially in the last two or three years.

"Throughout the year I've had chances (to win) but not been able to finish it off, so great to put that behind me now. Monkey's off the back now."

It was a disappointing ending for the 2022 British Open champion Smith, who was in an overnight share of the lead and hoping to become the latest Australian to win Asia's oldest professional golf tournament.

The 30-year-old, one of the biggest names to make the move to the lucrative Saudi-backed LIV Golf tour, shot a final-round two-under-par 68 to finish at 18-under.

"Pretty poor over the weekend," said Smith, who shot a 65 on Saturday.

"But I hung in there good, so lots of positives to take from that, but definitely wasn't the nicest golf to be played over the last couple of days.

"It didn't feel great, but it was still ok. Plenty of positives to take away from it, it was just a frustrating weekend."

Canada's hard-charging Richard T Lee and Phachara Khongwatmai of Thailand were joint third, two shots off the triumphant Campbell.

South Korea's Jang Yu-bin was fifth, with major winners Graeme McDowell and Patrick Reed 12th and 15th respectively.