Midway through their run-chase, the West Indies had done little to divorce themselves from the perception that they are lightweights in comparison to the Proteas as they stuttered to 115 for three in 21 overs in reply, leaving them with an unlikely 250 runs to win from 126 balls.
And there will be no cavalier innings from Chris Gayle to rescue them either as the big-hitting left-hander was out to the first ball of the innings.
Kyle Abbott sent down a rather wretched loosener, short and very wide outside off stump, which Gayle flashed at and umpire Sundaram Ravi called wide. The South Africans were convinced, however, that the batsman had nicked the ball and called for a review, receiving a positive verdict from third umpire Steve Davis.
Narsingh Deonarine and Dwayne Smith then added 77 from 77 balls for the second wicket, but it was hardly a hair-raising time for the South Africans with the comfort of such a large total on the board.
There was some disappointing bowling from Abbott in particular, but Wayne Parnell joined the fray in the eighth over and suggested that his game is there or thereabouts as he bowled three tidy overs for just nine runs.
There was some respite for the home side when Aaron Phangiso trapped Smith lbw for 31 with a straight one, and it all went horribly wrong for Deonarine in the left-arm spinner’s next over when he was run out for 43, losing his bat in the process as he tried to beat Hashim Amla’s whirlwind throw from short fine leg.
Marlon Samuels (22*) and Denesh Ramdin (11*) were working the ball around in a stand of 32 for the fourth wicket, but they had an awful amount of work to do if they were to challenge South Africa’s total.
Rain had delayed the start of play for two-and-a-half hours and saw the match reduced to 42 overs a side, and the West Indies won the toss and sent South Africa in to bat.
Rossouw helped himself to a career-best 132 off just 98 balls, with nine fours and eight sixes, and Amla cruised to yet another century, scoring a fine 133 off 105 deliveries.
Rossouw and Amla added 247 for the third wicket off just 181 balls, a record third-wicket partnership for South Africa and equalling their own mark for the best stand for any wicket that they set in the second ODI at the Wanderers.
It was another top-class batting display by the South Africans, even with big gun AB de Villiers having a rest, as they laid a solid platform on a tricky pitch and then launched a spectacular late onslaught.
A couple of wickets had fallen in the first 10 overs as Quinton de Kock (4) and Faf du Plessis (16) fell to horizontal-bat strokes on a pitch that provided enough awkward bounce to make those shots difficult.
Amla once again looked in a class apart as he reached a 49-ball half-century in the 21st over, midway through the innings with South Africa on 109 for two, while Rossouw, who has endured a troubled ODI career thus far, struggled through to his 50 off 60 balls.
But those early miscues all seemed a lifetime ago as Rossouw then blossomed in spectacular fashion, needing just 23 more deliveries to register his second century of the series.
The left-hander raced past Amla and looked every bit a power-hitter as he smashed 82 runs off his last 38 balls.
Amla just kept on amassing runs as he has all series, except in this innings he was able to do it in half-dozens at a time, clearing the boundary six times to go with his 11 fours, showing that even a great batsman like him has had room to improve his game.
The West Indies were bleeding runs horrifically as the sun shone brightest on its way to the western horizon, bathing SuperSport Park in a sepia light befitting a display that was one for the ages.
The last 147 runs of the Amla and Rossouw partnership came off just 69 balls … and that by two batsmen who are not renowned for being big boundary-hitters.
Finishers David Miller (23 off 9) and JP Duminy (18* off 7) were left with only a handful of overs to bat but they collected their share of boundaries as 87 runs were hammered in the last five overs.
With the bounce providing something for the bowlers to work with – which the West Indians failed to do – South Africa’s total is certainly well over par. But they will be wary that Chris Gayle is probably due a score in this series.