Klaasen hit 13 sixes in an awe-inspiring display of power hitting to help South Africa to a total of 416-5 – their second-highest against Australia – after they had been put into bat.
Australia replied with 252 in 34.5 overs and the disappointment of defeat will be multiplied by a hand injury to opener Travis Head that could rule him out of next month’s World Cup.
Head retired hurt after being struck on the hand by a rising delivery from George Coetzee in the ninth over, walking off the arena in obvious distress.
Australia were always going to be up against it after Klaasen’s innings had ensured a mammoth tally after a tepid start by the home side.
South Africa had scored 120-3 halfway through their innings, on an unusually slow wicket, and were looking at a mediocre total when Klaasen came to the crease.
He slashed a back-of-length ball for four with his third delivery and never looked back as he scored the second-highest ODI score by a No.5 batsman or lower - one shy of Kapil Dev’s record set against Zimbabwe at the 1983 World Cup at Tunbridge Wells.
Klaasen and Rassie van der Dussen, who made 62 off 65 balls, put on 74 quick runs for the fourth wicket as the hosts accelerated the run rate but it was Klaasen and David Miller who then feasted on the bowling.
Their partnership of 222 off 94 balls was the fastest double-century stand in ODIs. It ended with the last ball of the innings when Klaasen was caught in the deep.
His 174 came off 83 balls while Miller was unbeaten on 82 off 45 balls with Josh Hazelwood the best of the beleaguered bowlers with 2-79 off his 10 overs.
David Warner and Head have been in top form throughout the series but Warner departed cheaply on Friday, as Miller continued his heroics with a sharp close-in catch off Lungi Ngidi’s bowling.
After Head retired hurt, Marnus Labuschagne was dismissed as he gloved one down leg side to depart for 20 but Alex Carey and Tim David offered resistance with a 72-run partnership for the fifth wicket.
David’s dismissal effectively ended their chances. Carey hung on in search of his century but was the last man out, caught for 99 by a flying Quinton de Kock.
The series will be settled at the Wanderers in Johannesburg on Sunday.
