The 23-year-old finished 21-under to win the $3 million (£1.86m) event co-sanctioned by the OneAsia Tour by three shots from defending champion Nicolas Colsaerts of Belgium.
"I thought my first win was around the corner (this season).
To have three before May is literally unbelievable, but I've been playing well so I've been feeling like I can win and I've been giving myself opportunities," he said.
Grace not only matched the three titles Johan Edfors Of Sweden won in 2006 after coming through qualifying school but also became only the third South African - after Ernie Els and Retief Goosen - to win three times in a season.
Only two players - Seve Ballesteros (1977) and Sandy Lyle (1979) - have won three European Tour titles in a single season at a younger age.
Grace carded four birdies against a solitary bogey in his final round and maintained at least a two-shot cushion over Colsaerts who also returned 69.
"I stayed really calm today. I kept hitting the ball well. I missed a couple of shots the first couple of holes but regrouped well and made the birdies where it counts on the par fives, and just stayed with it from there," Grace said.
"I'm definitely here to win every week I play now."
Richard finch finished one shot behind after a final round of 66, while fellow Briton Ian Poulter finished 10-under after an identical card at Tianjin's Binhai Lake Golf Club.