PRETORIA, 15 Mar 2015 (AFP) - Playing on his home course, 28-year-old Coetzee carded a 65 to collect a second European Tour title after winning the Joburg Open last season.
The successor to Englishman Ross Fisher as Tshwane Open champion had earlier rounds of 67, 66 and 68 for a 14-under 266 total.
Blaauw finished second on 267 after rounds of 72, 65, 69 and 61 and South Africans Dean Burmester (67) and Tiaan van der Walt (67) shared third with Scot Craig Lee (70).
Coetzee edged ahead of Blaauw, who finished more than an hour earlier, with a birdie at 17 despite a wayward tee shot that landed in rough just short of the green.
A superb chip set up a birdie chance and 95-kilogram Coetzee holed the putt to move one ahead with one hole to go.
On the green in two at the bunker-littered par-four final hole, Coetzee curled his first putt close to the pin and dropped the next to pip Blaauw.
Coetzee birdied three front-nine holes and two on the inward trek in hot, partly cloudy conditions at the 6,458-metre (7,063-yard) layout.
"This victory is even more special than winning the Joburg Open," said Coetzee, "because my family and friends are here.
"Eighteen years of playing this course was very useful on the back nine today. I knew when to be aggressive and when not to be.
"Patience was a crucial factor -- I knew Jacques had finished 13 under and did not want to do anything rash while seeking to overtake him."
Blaauw failed by one shot to match the European Tour record single-round score of 60, which is shared by 17 golfers with European 2016 Ryder Cup captain Darren Clarke achieving the feat twice.
The South African birdied nine holes and did not drop a shot, then spent time relaxing, on the driving range, and practising his putting.
Northern Irishman Clarke closed with a 69 to finish nine shots adrift of Coetzee.
Leading Tshwane Open final-round scores Sunday at the par-70, 6,458-metre (7,063-yard) Pretoria Country Club (RSA unless noted):
266 - George Coetzee 67-66-68-65
267 - Jacques Blaauw 72-65-69-61
271 - Dean Burmester 65-68-71-67, Craig Lee (SCO) 67-68-66-70, Tiaan van der Walt 69-69-66-67
272 - Jaco Ahlers 69-67-70-66, Adrian Otaegui (ESP) 67-62-72-71
273 - Gregory Bourdy (FRA) 70-67-70 66, Robert Rock (ENG) 69-70-66-68