Australia spinner Ashton Agar grabbed a hat-trick as he stole the show in a thumping 107-run Twenty20 win over South Africa at the Wanderers.

Two years on from the ball-tampering scandal in Cape Town, which saw both Steve Smith and David Warner banned from the game, much of the pre-match focus was on the Australia star batsmen.

The duo were returning to action in South Africa for the first time since playing a part in that plot and experienced distinctly mixed fortunes with the bat, before Agar rose to the occasion.

The 26-year-old Agar reduced South Africa from an already unsteady 44-4 to 44-7 in their response to Australia's 196-6, removing Faf du Plessis, Andile Phehlukwayo and Dale Steyn, and there was no way back from there.

He remarkably later went close to a second hat-trick, finishing with career-best T20 international figures of 5-24 as South Africa were bowled out for 89.

South Africa put Australia in after winning the toss in the first game of a three-match series. Captain Aaron Finch made 42 and former skipper Smith top-scored with 45 as four other batsmen made at least 18 runs each.

Matthew Wade (18), Mitchell Marsh (19), Alex Carey (27) and Agar (20 not out) kept the scoreboard ticking over at a rapid rate, with Lungi Ndidi (37-1) and Kagiso Rabada (45-0) taking a carting.

Warner went to the second ball of the innings though, Steyn having the left-hander caught at long leg off at top edge.

Like Australia, South Africa lost an opener in the first over as Mitchell Starc bowled Quinton de Kock with a delicious delivery. But unlike Australia, South Africa did not find the rest of their batting order quite so dependable.

Du Plessis showed a modicum of resistance as chaos ensued around him, but his own dismissal was the beginning of the end for the Proteas - and the start of something special for Agar.

A mistimed shot against the left-arm slow bowler found the safe hands of Kane Richardson, before Agar secured an lbw verdict to remove Phehlukwayo.

Steyn took a lusty swipe at the hat-trick ball but only managed to find an edge and Finch took a fine slip catch, the ball hurtling his way.

Agar later bowled 33-year-old South Africa debutant Pite van Biljon at the end of the 12th over and had Ngidi caught at long-on from the first ball of the 14th, meaning that outrageously he was on the brink of a second hat-trick in the innings.

He was a whisker away from bowling Tabraiz Shamsi, but the batsman survived. Adam Zampa had the final say, bowling Rabada, but it was resoundingly Agar's day.