Campbell fired nine birdies at Yalong Bay Golf Club, with seven of them coming in a brilliant back nine of 29, to finish a stroke ahead of long-time clubhouse leader Chung Ye Na of South Korea.
"I hit a lot of good iron shots," Campbell said. "I had a lot of one or two-metre birdie putts and fortunately they all went in. My short-iron play was really good so I just had a lot of opportunities.
"This year I haven't played that good golf but I went home with my coach and worked on a few things. I live in Canberra and my coach Gary Barter is in Sydney so I've got to drive for three hours, get a lesson and then drive home.
"Even on the range this morning I was like, 'It feels okay, but I'm not sure how it will go.' I felt comfortable out there and hit a lot of shots close.
"I was lucky to get into this event. I was given a sponsor's invitation so I was very grateful to be coming to China and to be playing."
Chung also returned a flawless round with eight birdies and no bogeys, while England's Charley Hull was among six players sharing third place on five under after a 67.
"It was pretty simple out there, fairways and greens and I holed a few putts," said Hull, who finished second in each of her first four events on the Ladies European Tour earlier this season. "The greens have become better as the week's gone on and are rolling quite nicely now, so it's good.
"I'll try and pick up a win but if not I'll try next year. I'll carry on enjoying it and I'm looking forward to Christmas soon. I'm looking forward to the end of the season now to work on a lot of stuff."
Compatriot Laura Davies was a shot behind Hull on four under alongside Scotland's Kylie Walker.