That left him just 137 metres to the flag and the 21-year-old hit a pin-point pitching wedge to 18 inches from the cup for a tap-in eagle-three – the perfect way to start his round.
In terms of his day, it was the shot that got him going and he would shoot a splendid, bogey-free six-under-par 66 on the challenging 7,020m lay-out.
It was also an encouraging bounce back to form for him after missing the cut in the two other European Tour events he’s played in this summer – the Alfred Dunhill Championship at Leopard Creek at the end of November and last week’s BMW South African Open at Glendower.
Porteous said it was 22-year-old Brandon Stone – his great rival from his amateur days and winner of the SA Open on Sunday – who taught him a valuable lesson.
“Hats off to Brandon and I can’t thank him enough because his win was a blessing in disguise for me. The point is he works so hard and deserves all he gets. And I came to realise that, compared to him, I was practising like an amateur in a professional game.”
Both Porteous and Stone were ranked number one in South Africa as amateurs.
“In those days I’d tee up pretty much knowing that everyone else would be playing for second,” says Porteous. “Since I joined the pro ranks I’ve come to realise that I can’t just rely on my talent.
“I’ve got to work much harder and smarter on my game, and be more disciplined by getting up at a certain time and going to gym.”
This new dedicated approach certainly reaped its rewards on Thursday.
His 66 was the best round of his pro career, Porteous said after joining a six-way tie for second in the Joburg Open.
It also reminded him that it was he who had got the better of Stone in the Barclays Kenya Open on the Challenge Tour last year when he beat him with an eagle in a sudden-death play-off for the title.
“I know I can play this game and seeing Brandon win at Glendower was a reminder to me that I too belong.”