It was also a promising start for the Scots at Sun City, where Richie Ramsay led the way and David Law, Ewen Ferguson, Scott Jamieson, Connor Syme also broke par, with Bob MacIntyre being the odd man out.
Fox, who landed his second win of the season in the Alfred Dunhill Links Championship on Scottish soil last month, could leap above McIlroy at the top of the standings with a win this week.
Bidding to become the first Kiwi to be crowned European No 1, he was level-par for the day after eight holes before sparking his round with a birdie at the ninth and, helped by an eagle-3 at the 14th, storming home in 29. “I couldn’t have wished for a better start,” said Fox.
He leads by a shot from European Ryder Cup captain Donald, who shook off his lowly 245th position in the world rankings to card a bogey-free opening effort, which included three birdies in the last four holes. “A little bit unexpected, to be honest,” said the Englishman of his effort.
Ramsay sits in a tie for seventh after a 69, one better than Law while Ferguson, who was playing alongside Donald, Jamieson and Syme all signed for 71s. Wearing a bucket hat to combat the conditions, MacIntyre signed for a 73.
“It was hot today,” said Ramsay, who won the Cazoo Classic at Hillside in the summer. “It was the first real day where the heat was there and this is what I remember the Nedbank being like and you feel your legs when you come off.
“Obviously with the comes the ball flying that bit further and there was lots of steady golf in there and I hit some shots really well as the wind can swirl like crazy here.
“The big thing was I hit a lovely chip on 16 and 17 then got up and down at the last, so that gives you huge momentum going into tomorrow rather than shooting level and feel you’ve played really good but not made the most of it.”