Little-known outside his home country a year ago, the new sensation of the European Tour added the Dunhill Links Championship at St Andrews to his amazing list of achievements.
"It feels awesome," said Grace, who has risen from outside the world's top 300 to inside the top 40 and might even yet deny number one McIlroy the European money list title next month.
He is up from 12th to third and added: "It's definitely in my sights."
Grace, who began the week with a Tour record-equalling 60 at Kingsbarns, claimed the £491,000 first prize with a tournament record 22-under-par total.
But if starting the final round with a four-stroke lead and ending it two ahead of Dane Thorbjorn Olesen sounds a comfortable day's work, then think again.
After the Pretoria golfer dropped a shot on the seventh, Olesen birdied the next two and when Grace three-putted the short 11th for another bogey they were level.
It was then, however, that he showed the class that had already brought him the Joburg Open, Volvo Champions, China Open and, on his home circuit last Sunday, the Origins of Golf titles in 2012.
Grace birdied the following three holes from 10, 12 and 14 feet and when Olesen bogeyed the next, the gap was back to four.
Even then it was not a cruise to the line.
Olesen birdied the 16th and he bogeyed the Road Hole 17th, but when Olesen came up a fraction short with his eagle attempt through the Valley of Sin on the last, Grace had two putts for victory from four feet - and needed only one of them.
It made him the first wire-to-wire winner of the Tour season, but was the second time he has won back-to-back.
Like Louis Oosthuizen and Charl Schwartzel, Grace is a product of the Ernie Els Foundation and the current Open champion has already tipped him to be another major champion.
Winning at the Home of Golf, as Oosthuizen did in the 2010 Open, will do for the time being, though.
"I've really dreamt of this moment my whole life," he said. "I had goosebumps thinking this morning [Sunday] about Louis and the possibility of holding a trophy here myself.
"It was a tough day, but the putter started working and that's all I needed to do."
Grace's caddie Zack Rasego was on Oosthuizen's bag two years ago and, after asking him to start reading the lines with him on the back nine, he took control again.
Using a new driver after his usual one cracked last week, Grace shot a closing 70, while Olesen's 68 left him two ahead of Swede Alex Noren.
Scot Stephen Gallacher, whose only Tour victory in nearly 400 starts came in the event eight years ago, finished in a seven-way tie for fifth after running up a quadruple-bogey eight at the 16th.
The 37-year-old, lying fourth on his own at the time, went to what he thought was his drive and hit it, only to discover it was actually the ball of Danny Willett's amateur partner Steve Halsall.
It cost Gallacher a two-stroke penalty and his was then found in the left-hand rough.
"It never even crossed my mind because he was looking 50 yards further up. Obviously I'm a bit disappointed, but what can you do?"
He also incurred a penalty in Thursday's opening round when, in taking a practice swing, he clipped a divot and it hit his ball.
Gallacher still earned £81,415, but with a par on the last hole he would have taken home a cheque for £184,660.
Three of the victorious European Ryder Cup side were in the field, but Martin Kaymer and Peter Hanson both managed only 34th place, while Paul Lawrie missed the cut.