Firdose Moonda is ESPNcricinfo's South Africa correspondent
Australia 196 for 6 (Smith 45, Shamsi 2-31, Steyn 2-31) beat South Africa 89 (du Plessis 24, Agar 5-24) by 108 runs
Ashton Agar claimed the 13th hat-trick in T20I cricket and the second for Australia after Brett Lee as South Africa were dismissed for their lowest score in the format to lose by their biggest margin in a thrashing at the Wanderers.
Agar finished with a career-best 5 for 24 to take Australia to an eighth straight T20I win, and to the top of the ICC's rankings. They extend a successful run that dates back to February 2019, and take the lead in the three-match series.
While South Africa's batting implosion will hog the headlines, their fielding should also come under scrutiny after a wayward performance, with too many short, wide deliveries against a rampant Australian line-up. Aaron Finch and Steve Smith galloped along at 10 runs an over in a second-wicket stand of 80 and even though South Africa pulled Australia back, 49 runs in the last five overs left them with a big total to chase.
The home batting line-up, which had a makeshift opener in Rassie van der Dussen, and an emergency replacement in Jon-Jon Smuts (who stood in for Heinrich Klaasen after he injured his hip in warm-ups) never got going. South Africa were 38 for 3 after the powerplay, 44 for 7 after Agar's hat-trick and only had three partnerships in double figures.
Agar, Agar, Agar
Faf du Plessis's inside-out loft over the side found Kane Richardson on the rope to end the most competent innings by a South African frontline batsman at the Wanderers and start a magical run for Australia's left-arm spinner. His next ball was pitched on middle and leg and beat Andile Phehlukwayo's flick and was given out by Allahudien Palekar. Phehukwayo reviewed but ball-tracking showed the delivery was straightening and hitting leg stump. That brought Dale Steyn to the crease, in the eighth over, to face the hat-trick ball.
He was greeted with a ball that was tossed up, went for the drive and outside edged to Aaron Finch, at slip. Agar took off in celebration and South Africa, on 44 for 7, had all but been defeated. Agar could have another hat-trick when he bowled debutant Pite van Biljon at the end of his third over and had Lungi Ngidi caught at long-on with the first ball of his fourth, but his second hat-trick ball of the night missed Tabraiz Shamsi's off stump by a whisker.
Steyn's alive…but so are the lights
Dale Steyn operated mostly behind the scenes in the England series but stormed his way back into the spotlight in the first few balls of this match. His opening delivery was a touch wide and David Warner creamed it through the covers to start with a boundary. That would not have impressed Steyn, who tightened up immediately and sent down a menacing second ball, a bouncer that fizzed up off a length, Warner top-edged and Shamsi collected at fine leg. Steyn celebrated in his customary fashion - the chainsaw - but in slow-motion, perhaps as a nod to his advancing age.
But he won't like the suggestion that his years had anything to do with his inability to repay the favour when fielding in the next over. Ngidi should have had Smith out for a duck when he cut a short, wide ball to third man, where Steyn was stationed. He got himself into position to take the catch but lost the ball in the floodlights at the last moment and it sailed over his right shoulder. When Steyn realised what had happened, he could only smile sheepishly in response. Steyn eventually made up for it in the penultimate over of the match when he made sure Ngidi did not finish wicketless and clung on to a high ball from Mitchell Marsh's bat at square leg.
Slowly does it for South Africa
The spin of Shamsi and Smuts - in addition to Andile Phehlukwayo's change-ups - pulled Australia back in the mid-section of their innings, when they kept big hits to a minimum. The boundary was only breached three times between the end of the sixth over and the end of the 14th, once when Matthew Wade should have been caught on the deep midwicket boundary by van Biljon. Shamsi conceded a slog sweep that went for six towards the end of his spell, where wides were his only weakness, while Smuts' two overs cost just 15 runs and he should have been used a little more. South Africa gave away 61 runs in those eight overs, at a rate of 7.62, which kept Australia under 200. In the end, it was still more than a hundred runs too many.
Starc's crucial breakthrough
With moisture in the air, it was inevitable that would be some swing but it wasn't until Mitchell Starc got hold of the ball that it was on display. His third delivery was directed straight at de Kock, who looked to play leg side, snuck past his attempt and pinged the top of middle stump. That meant South Africa's most in-form batsman of the summer was out, and the rest of the line-up had a mountain to climb.
Agar took the honours but it was Australia's fast bowlers who did the early damage and reduced South Africa to 38 for 3 in the powerplay, leaving them with no way back. After Starc's early strike, Pat Cummins was responsible for the other two wickets and had van der Dussen caught at third man and Smuts caught by Adam Zampa, running circles from short-fine leg. Australia scored 70 runs in their first six overs and South Africa's score, of just over half that, was never going to be competitive enough.
Fielding fumbles and Faf
Steyn's miss was comical, van Biljon's may be explained away by debut nerves but Shamsi's miss in the final over was inexcusable. Agar top-edged Rabada to short third man, de Kock looked to be going for it as Shamsi ran in which made the keeper think twice. At that point, Shamsi should have committed to the catch but he pulled out and the ball fell between him and de Kock.
It wasn't all bad, with du Plessis taking a stunner at backward point when Carey launched one into the night sky, but that was a rare bright moment in South Africa's effort, compared to a clinical Australian display.
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Ball-by-ball commentary of Ashton Agar's hat-trick and five-wicket haul in Johannesburg
Ashton Agar hat-trick, five-for sends South Africa to record defeat
South Africa fell to their lowest T20I total as Ashton Agar ripped through them at the Wanderers