Heinrich Klaasen slammed a 54-ball century as South Africa beat the West Indies by four wickets in the third and final one-day international on Tuesday. 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).