Muller's bogey-free effort left him a shot clear of Canadian-based Scotsman Doug McGuigan and South Africans Richard Kaplan and Bradford Vaughan, the runaway winner at last week's Investec Royal Swazi Sun Open.
Darren Fichardt, who ended his round with four straight birdies, was one of a quartet on 66, which also included highly rated amateur Dean Lambert, who had six birdies and just a single dropped shot over the testing par-71 lay-out. In fact, it was a brilliant first day for the trio of amateur invitees, with both Richard Sterne and Jaco van der Merwe carding 69s.
But with 42 of the field of 75 returning scores of level par or better, Els and McNulty suffered the rare indignity of being among the first day also-rans. The 'Big Easy', who indicated he's struggled off the tee, was five over par for his round after a double-bogey six at the 10th, where he hit his drive 'way right' - 'I didn't even go and look for that one,' he said later - but an eagle three at the 13th and a rare birdie at the 15th got him back to a two-over-par 73.
McNulty also struggled early and was three over through seven holes, before making two birdies for a 72.
By contrast, 30-year-old Muller began in sensational fashion, with five birdies in a row, to cruise into an early lead. After that, he managed two further birdies, at the two par-fives on the back nine, the 13th and 18th.
Muller, who said he had developed a spasm between his shoulder blades on Wednesday evening and had got his (unnamed) room-mate to give it a rub, said the new lay-out was 'a hell of a tough course.'
'When I first looked at it, it looked to me like the toughest course I'd ever played. You can make this far tougher than Sun City,' he said. 'What made it a bit easier for me today was that I didn't miss a fairway.'
Muller, who has always worked to supplement his golf, as a teacher, an insurance salesman and in his own paint contracting business, said the current Sunshine Tour was 'the first year I've not worked and played and it has paid off.' He's still doing some teaching, but has confined that to certain hours in the day and is very much focussed on the professional game.
Not one of the longer hitters on the Tour, Muller said he preferred courses to be tougher, punishing shots that missed fairways, rather than allowing the big hitters to spray the ball off the tee 'and always have a shot.'
Noting that Leopard Creek was just such a lay-out, he said he fully expected 'to see McNulty up there by the end of the week.'