While Lawrence earned his breakthrough victory it was Clark who nearly walked away with the tournament.
The South African took a one-shot lead over fellow countryman Lawrence after rolling in a 15-foot putt to save par at the 16th, a hole Lawrence bogeyed.
Clark ran into trouble on the following hole after his drive found a fairway bunker. He had a difficult lie and was only able to blast out short of the green. His third shot ran over the putting surface while his fourth set up a two-putt for double-bogey.
He fell out of the lead and relinquished the championship to Lawrence but walked away with the Order of Merit title.
'I couldn't believe what happened at the 17th,' said Lawrence. 'When Tim was two shots clear of me I thought he was going to run away with the tournament. But after 17 I thought, 'Oh my gosh, I can win this tournament'. But my heart goes out to Tim. He really gave it everything out there.'
Clark came into the Tour Championship with only a slight lead over Justin Rose in the race for the money title. After both players shot 3-under 69 in the opening round, Clark distanced himself with two more rounds in the 60s while Rose struggled to a 2-over 74 in round two.
Rose never made up the difference closing with a 3-over 75. The South African Masters winner never felt comfortable at the Leopard Creek Country Club finishing at 1-over 289 for the tournament.
Clark earned his PGA Tour card last year after finishing third on the 2000 Buy.Com money list. He missed most of the 2001 campaign due to a wrist injury and was granted a medical exemption for 2002. The 26-year-old delayed his return to the PGA Tour after his win at the South African Open put him in position to win the Order of Merit, a decision that paid off.
Along with the money title, Clark earned an entry to the British Open and the World Golf Championships American Express Championship.
Lawrence left the door open for his challengers to take the lead Sunday, but in the end the he played well enough to earn his first win.
'I'm dumbstruck. I can't believe what's happened. It hasn't sunk in yet,' he said.
The 21-year-old bogeyed the first hole to fall into a tie with Clark but responded well with birdies at Nos. 3 and 5 to make the turn at minus-14.
He climbed to 15-under after a birdie on the 11th but ran into trouble with his second bogey of the day at the par-3 16th.
Lawrence's maiden victory also came with incentives as the young South African earned a spot in the World Golf Championships NEC Invitational.
'Is Tiger playing in that tournament,' asked Lawrence. 'Oh my word, I'm going to be playing in the same tournament as Tiger Woods.'
Vaughan, the second-round leader, kept pace with four birdies to climb to 14-under before dropping a shot on the same hole as Lawrence, the 16th.
The South African duo of Nic Henning (68) and Andrew McLardy (69) shared fourth at 12-under 276. Fellow South African Hennie Otto (72) finished one shot further back at 11-under.
Full-field scores from the South African Tour Championship