Australia 6 for 307 (Khawaja 138*, Smith 59, Handscomb 54, Abbott 3-38) lead South Africa 9 for 259 dec by 48 runs
Scorecard and ball-by-ball details
In his first innings as a Test opener, Usman Khawaja scored Australia's first hundred of the series, and their first in day-night Test cricket. In his first innings as a Test batsman, Peter Handscomb scored an impressive half-century. In his first innings as a Test batsman, Nic Maddinson was bowled for a duck. Such was the progression for Australia on the second day in Adelaide, where South Africa used the second new ball to fight back late in the evening.
Most of this day belonged to Khawaja, who batted throughout it and by stumps had occupied the crease for 285 deliveries. But the last session was arguably South Africa's as they claimed three wickets and reached into Australia's tail, although a frustrating seventh-wicket stand between Khawaja and Mitchell Starc prevented them running through it. At stumps Starc had 16 and Khawaja was on 138, ready to take his innings into its third day.
Khawaja was hoping the tail would help him build a big enough lead to worry South Africa - already the advantage was 48. Australia scored 95 runs in the first session, 100 in the second and 98 in the third and if runs did not come exactly briskly - Kyle Abbott was especially frugal and picked up 3 for 38 from 25 overs - a batsman could rotate the strike and pick off the bad balls once settled, as Khawaja did brilliantly.
Khawaja was so patient that his first 80 deliveries brought only 18 runs. Perhaps it was a blessing in disguise for Australia that David Warner was prevented from opening on the first evening because he had spent too long off the field having treatment on his shoulder. The tricky period before stumps on day one required watchfulness, and Khawaja carried that trait into the second day as Abbott especially asked questions of the top order.
The debutant opener Matt Renshaw (10) and then Warner in the unfamiliar position of first drop both edged Abbott to third slip where Dean Elgar held both catches, the first so low to the ground it needed third-umpire confirmation and the second more at a more comfortable height. Australia were 2 for 37 and the innings could have gone either way. As it happened, Khawaja and Smith steadied perfectly by putting on 137 for the third wicket.
Smith was dropped on 46 when he edged JP Duminy and Hashim Amla at slip juggled and dropped the chance, and the partnership only ended via a communication breakdown between Smith and Khawaja. On 59, Smith pushed Tabraiz Shamsi to point and called for a single. Khawaja set off before calling no and Smith seemingly did not hear and kept running. By the time he had stopped and tried to regain his own ground, it was too late.
But if you're going to sell the captain's wicket cheaply you should at least put a high price on your own. Khawaja did that, and brought up his fifth Test century from his 197th delivery with a cut through point for four off Shamsi. He was prolific through the leg side, pulling well when the bowlers dropped short, and once he became used to Shamsi's wrist-spin he used his feet and drove exquisitely through cover.
He followed his century stand with Smith by compiling a 99-run partnership with Handscomb, and it continued Khawaja's fine series - he has featured in seven of the 10 Australian stands of 50 or more in this series. But Handscomb was equally impressive during their time together at the crease. His first ball in Test cricket was a pearler from Vernon Philander that moved away just a fraction and beat the outside edge, but Handscomb survived and thrived.
His method of batting deep inside his crease gave him time to cut effectively and he also used his feet to the spinners. He appeared unawed by the occasion and ensured the strike was rotated, in fact outscoring Khawaja by 14 runs during the stand. Handscomb struck six fours and three in succession off Philander brought up his fifty from his 70th delivery.
In the end it was Abbott who breached Handscomb's defences, seaming the new ball sharply in to bowl him for 54. As one debutant walked off another walked on, but where Handscomb had been calm and in control, Maddinson struggled to get his feet moving and finished with a 12-ball duck when Kagiso Rabada swung one in a searing yorker that rattled the stumps.
In the next over, Philander had Matthew Wade caught behind and at 6 for 283, there was a risk Australia would collapse and their lead would be minimal. But by stumps, Starc had survived for 50 deliveries and frustrated South Africa's hopes of a quick finish to the innings. And, as ever throughout the day, Khawaja was still there.

Brydon Coverdale is an assistant editor at ESPNcricinfo. @brydoncoverdale