Watson, who is yet to break through on the South African Golf Association’s provincial circuit, reeled in five birdies and an eagle at Walker Park Golf Club to edge ahead of Angus Cole-Ellis from Ekurhuleni.
Recent Southern Cape Open champion Carlo O’Reilly lurks three off the pace alongside Luke Trocado from Western Province.
Boys Amateur Championship semi-finalist Keegan de Lange from Gauteng North carded a 69 to tie for fifth with yet Jade Buitendag from Southern Cape.
KwaZulu-Natal-born Watson spent six years at Fancourt before his family relocated to St Andrews in Scotland in 2012. The 2014 St Andrews Links Junior Golf champion returned to George last year.
Watson followed a pair of birdies at the first and second holes with seven straight pars to turn two under, but caught fire on the back nine.
The 19-your-old Fancourt golfer boxed an eagle putt at the par-five 10th, birdied 11 and closed with another pair of birdies to finish the back nine in 31 strokes.
Cole was equally impressive with seven birdies, including three around the turn, but spoiled his chances to tie for the Watson lead with a bogey at 13.
O’Reilly also dropped a shot at 13, but countered with birdies at two, seven, 10, 12 and 17.
Trocado burst from the blocks with a hat-trick of birdies.
Having wiped out his good work with a double bogey six at four and a bogey at five, the Atlantic Beach golfer hit back with an eagle at the par-five sixth and another eagle at 10. He dropped another shot at 12, but atoned for the mistake with a birdie at the closing hole.
FIRST ROUND SCORES – TOP 20
65 Tom Watson
66 Angus EllisCole
68 Carlo O’Reilly; Luke Trocado
69 Jade Buitendag; Keegan de Lange
70 Marco Steyn; Ryk Lacock; Albert Venter
71 David Meyers; Werner van Wyk; Sean Bradley; Jan Combrink; Brandon Gildenhuys
72 Dean Martin; Theunis Bezuidenhout; Quintin Wilsnach; Neal Herman
73 Byron Sampson; Jason Smith; Andrew Plint; Shaun Bernstein