Immelman followed up his Saturday 66 with a seven-birdie effort that now solidifies him as a legitimate young star on the European Tour.
Clark, who had a horrible quadruple bogey nine on Saturday to bring the field back into the tournament, carded a 3-under-par 69 on Sunday that would have been good enough for the win, if not for the dreaded nine on Saturday .
'That was four or five shots wasted in one hole,' said Clark, referring to 16 in the third round. 'It's just one of those things. I could have hit the first chip 25 feet past the hole and escaped with a par five, but I was trying to get it close for birdie. With a bit better thought process, things would have been different.'
But Immelman birdied the 72nd hole to force the playoff that ultimately denied his compatriot, Clark, the chance to become the first player since Gary Player back in 1977 to repeat as champion.
'I've been dreaming of this moment for so long, and for it to happen in front of my home crowd, people whom I've known forever, is difficult to take in. I don't really have the words to describe how I feel. It's just incredible.'
Immelman, just 24 years of age, led a pack of no less than seven players that hailed from the host country to finish on top of the leaderboard.
Third round leader Jean Hugo had a disastrous collapse late in his round that cost him a spot in the two-man playoff. Coming to the 16th with a share of the lead, Hugo proceeded to make bogey, then double bogeyed the 17th to keep him from winning his first ever tournament.
'I thought I had a good chance of winning' said Hugo, who lost his European Tour card at the end of last season. 'What happened on the 16th was disappointing but I tried my best and have another co-sanctioned event in Johannesburg this week to try to regain my card.'
Justin Rose could only muster a 1-under 71 that dropped him back into a tie for eighth, four shots off the pace. A triple bogey at the par-4 fourth dashed any hopes of collecting his third Euro title.
Fortunately for Rose, there will not be a whole lot of time to worry over the 'what ifs,' as he is set to defend his title at the Dunhill Championship next week in Johannesburg.