Campbell, who is 635 on the world rankings, drained a 15ft birdie putt on the 18th hole to top playing partners Smith and Thailand’s Phachara Khongwatmai who earlier caused a bizarre 20-minute delay.
Campbell had not led at any stage of the tournament until his last putt to finish at 19 under par and beat Smith by one and Phacahara by two.
For Campbell, who also birdied the 17th, it was his maiden win on the Asian Tour with his only other win in the professional game coming at the New Zealand PGA Championship in 2018. He won $US360,000 ($NZ611,000).
“It’s good to finally get the monkey off the back and yeah, sort of just battling away all day,” said Campbell.
“Sort of didn’t get off to the greatest of starts and swing wasn’t feeling that great. Sort of went back to a few close losses and wrote a few notes down in my yardage book last night, and really used them on those last four or five holes.
“It was getting a bit tight in the swing and just from those past experiences managed to, I think, you know, put a couple of nice swings coming down the stretch which really helped.”
The victory is also just reward for a player who has struggled with injuries and missed six months last year due to a back issue that required surgery.
“Even probably four months ago I was sort of battling with the body. I’ve had quite a few operations, and bulged discs in the back and things like that, so had to change the swing quite a bit, especially in the last two or three years. So yeah, great to put that behind me now and the monkey’s off the back which is good.”
The most recent Kiwi winner of the Hong Kong Open was Frank Nobilo in 1997, while the only other was Walter Godfrey in 1972.
Smith and Phachara had started the day sharing the lead with Campbell one back.
Phachara looked to be heading for the win when he birdied three in a row from 11 and led by one from Smith and two from Campbell with three to go.
However, drama unfolded on the par-four 16th when he hooked his tee into the trees. He chose to try to hit his ball back into play from a treacherous lie but failed to get it out before just being able to advance his ball to the edge of the fairway with the next.
Smith and Campbell appeared visibly irritated by Khongwatmai’s actions, which led to a 20-minute delay.
“He can’t stand all over this, can he?” Campbell was heard saying to officials.
While Khongwatmai selfishly sought relief from his lie in the bushes as his playing partners had to wait, Smith and Campbell protested.
"He's broken these branches here," Campbell told officials, to no avail, while pointing to the vegetation in question. "Look at that, these just got broken ... Wow."
As Smith walked away, seemingly in dismay and disgust while possibly also trying to retain focus, international TV commentators couldn''t believe what they were witnessing.
"I've never seen this before," one said.
"You get the impression his playing partners are not happy."
Eventually, after some 20 minutes of delay, Khongwatmai - down on his knees with no sight of the ball after changing clubs twice - attempted his shot.
"He's not thinking clearly," a commentator said. "I really don't think he is. This could go horribly wrong. His head must be in a mincer at the moment."
Phachara ended up making a costly double. He also birdied the next hole before his disappointing finish on 18.
“Today my putting was not so good like the last three days, but I played well since the beginning until the 16th hole,” said Phachara.
“I was in a very difficult situation at that moment that I couldn’t do anything. Also, there were broken trees, which was an obstacle, so I couldn’t step backwards to drop the ball. I had to keep trying to hit it. However, I’m satisfied with my overall performance that I can make under par for today.”
- with AAP