It seemed like a situation tailor made to expose Dawid Malan's perceived faults. Chasing 192, England were 25 for 1 in the fourth over, on a Newlands pitch that was supposed to be slow and worn. Surely, this would be the occasion that his penchant for scoring slowly at the start of his innings would catch up with him, and his T20 international form would begin to revert to the mean.
Instead, Malan pulled his first ball through square leg, flashed his second through third man and pulled his third over fine leg for six. England's notorious slow starter was on 14 off 3.
Perhaps, then, the real test would arrive when he came up against Tabraiz Shamsi, South Africa's animated left-arm wristspinner. Shamsi had bowled 14 balls to Malan in his T20 career, conceding only 12 runs and dismissing him once. The fact that Shamsi's stock ball turns away from a left-hander's bat made him an obvious bowler for Quinton de Kock to use, creating a match-up that should have suited South Africa.
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In fact, Malan reverse-swept Shamsi's first ball for four. In the second over he faced from him, he swept another four; in the third, he lofted him inside-out over extra cover before slog-sweeping him over midwicket.
Shamsi's fourth over was the best of the lot for Malan: another reverse-sweep for four, another booming drive over the cover ring, and a violent crack dead straight back over the bowler's head. Malan faced 14 balls from the bowler that was meant to trouble him the most, and hit him for 38 runs.
There is no clearer sign that a batsman is in a rich vein of form than the cover drive being his most productive shot. No prizes for guessing that 30 of Malan's 99 runs came in the area between cover and extra cover, 20 of them via sumptuous boundaries.
This was an innings to dispel any lingering doubts about his spot. Throughout Malan's T20I career, there has been a sense that for all his success, his time in the side would be fleeting. With England rarely fielding a full-strength XI in T20I cricket, instead prioritising the 50-over team, it has been difficult to work out exactly where he stands within the set-up.
In early 2019, he flew to the Caribbean hoping to "prove a point" in a T20I series against West Indies, at which point he had made four fifties in five innings; he didn't play a game. Later that year, after hitting only England's second hundred in the format, he was implicitly criticised by his captain for failing to run a bye off the last ball to protect his average.
Earlier this year, he wrote in a column for Sky Sports, "I don't know how you can be under pressure with numbers like [mine]" immediately before three T20Is in South Africa; he was given one game, out of position at No. 4. This summer, as he became the ICC's No. 1-ranked T20I batsman, he found himself criticised for his slow starts - including on this website. Before this series, many wondered if he would eventually drop out of the side to accommodate Joe Root ahead of next year's T20 World Cup in India.
But after his Cape Town effort, there can be little doubt about it: Malan has proven unequivocally that he is in England's best T20I side. His average remains over 50, with his strike rate a tick under 150; he has passed 50 in more of his 19 innings than he has not. Having initially seemed like something of an outsider, attracting little praise from his team-mates, he now has their full support.
There may still be challenges to come, of course. Malan is highly likely to be sought after at the next IPL auction, and his game against spin and high pace will come under scrutiny in that tournament. There is still the best part of a year until the T20 World Cup, and as Jason Roy's struggles in this series have demonstrated, the vagaries of form can catch up with anyone.
And yet there remains a sense that even if his form slumped dramatically in the T20 circuit, he would manage to turn things around in an England shirt. Malan has cited the quality of pitches and the amount of extra preparation that he feels he is afforded at international level as the reason behind his England record outstripping his numbers in domestic T20 cricket, and on this evidence it is hard to question his judgement.
The clearest evidence yet of his improved standing in the dressing room came immediately after he had nudged the winning run into the off side to leave himself on 99 not out. "I didn't know how it would go down if I turned down the single," he smiled at the post-match presentation, with Morgan lurking over his shoulder. They were not the words of a man fearing for his place.
England's players have repeatedly stated over the last few months that there is no harder task for a professional sportsman than to force your way into their white-ball teams. It is testament to Malan's performances that he has managed to do just that.