But Struver's drive landed in a divot and he hit his nine iron into the water hazard to the left of the green. He finished with a six, for a three- over-par 74.
South African Frost's 68, one of only five sub-70 rounds on the final day, gave him the pounds 100,000 first prize, one shot clear of American Scott Dunlap and Jeev Singh of India as Struver had to settle for fourth place.
"My drive was perfect on the 18th but it went into a divot and from there the ball could have gone anywhere," said Struver. "It was just bad luck."
Frost found the water himself on the par five 12th, but still managed to save par after taking a drop and chipping 50 yards to two feet.
"I had a vision right from the start of this tournament of the crowd sitting in the stands watching me win," said Frost, who learned the game at the Stellenbosch Golf Club.
The defending champion Ernie Els, who also started the day four shots off the lead, was never in contention. He shot 72 to finish joint sixth.
In Florida, the British pair Laura Davies and Helen Dobson overcame the threat of thunderstorms to move into contention after the third round of the Naples LPGA Memorial.
Davies packed six birdies into a 68 while Dobson had a 67 and they both finished on eight-under-par 208, four shots behind the joint leaders, Karrie Webb, the two-time British Open champion from Australia, and America's Juli Inkster.
Scotland's Brian Barnes improved on his opening 73 by five shots at the Mastercard Championship in Hawaii for a three-under-par two-round total of 141. Barnes is eight strokes behind the leader, John Jacobs, who holds a three-shot advantage over Ray Floyd.Reuse content