Heinrich Klaasen slammed a 54-ball century as South Africa beat the West Indies by four wickets
South Africa were in trouble at 87 for four chasing a West Indian total of 260 but Klaasen went for his shots and the home side chased down the target with 20.3 overs to spare.
The series was shared 1-1 after the first match was rained off.
"We try to play conditions and not the situation and the conditions were fantastic," said Klaasen.
Klaasen finished with 119 not out off 61 balls, hitting 15 fours and five sixes in Potchefstroom. He shared partnerships of 55 off 38 balls with David Miller (17) and a match-clinching sixth-wicket stand of 103 off 62 deliveries with Marco Jansen (43).
ALSO READ: Shoaib Akhtar predicts an India-Pakistan final at World Cup 2023
"It was a good wicket and it was one of my better knocks," said Klaasen after notching his second one-day international century and the fourth-fastest for South Africa behind two from AB de Villiers one from Mark Boucher.
De Villiers holds the world record with his 31-ball hundred against the West Indies in Johannesburg in 2014/15.
Alzarri Joseph rocked the South Africans at the start of their innings by taking the first two wickets with aggressive, short-pitched bowling.
He finished with three for 50 but the rest of the West Indian bowlers took heavy punishment.
Klaasen was particularly severe on spin bowlers Akeal Hosein, who took two for 49 in seven overs, and Yannic Cariah, who conceded 49 runs in 3.3 overs.
West Indies were bowled out for 260 after they were sent in by Aiden Markram, captaining South Africa in the absence of Temba Bavuma, who had a hamstring strain.
Brandon King struck 11 fours and a six in making 72 off 72 balls in an innings studded with elegant drives.
But the rest of the West Indian batsmen failed, apart from Nicholas Pooran, who hit 39 and Jason Holder, who made 36.
"We batted well in parts but we definitely did not perform with the ball," said West Indies captain Shai Hope.
The series did not count for the World Cup Super League but Markram said Tuesday's result was important ahead of two matches against the Netherlands at the end of the month which South Africa must win if they hope to qualify automatically for the World Cup.
"It's nice to get momentum going into those games," said Markram.