South Africa 6 for 194 (Cook 81*, Lyon 3-48) lead Australia 383 (Khawaja 145, Smith 59, Handscomb 54, Starc 53, Abbott 3-49, Rabada 3-84) by 70 runs
Scorecard and ball-by-ball details
By the time Nathan Lyon took his first wicket of this Test, he had endured a 660-ball drought without a first-class breakthrough. He was lucky even to be playing, for only Steve O'Keefe's calf injury saved Lyon from the axe, prevented the Goat from becoming the Scapegoat. But on the third evening Lyon reminded Australia's selectors why he has become Australia's most prolific offspinning Test wicket taker, his three strikes tightening Australia's grip on the match.
Between Lyon and Mitchell Starc, who bowled with pace and aggression and picked up two wickets, and Josh Hazlewood, who removed Hashim Amla for the fifth time from five innings in this series, Australia kept South Africa on the back foot. South Africa started with a deficit of 124, which by stumps had become a lead of 70. But with only four wickets in hand, a great deal of work remained for it to become the kind of target that would worry the Australians.
If you asked the Australians this morning which South African batsman would annoy them most today, they might have said Faf du Plessis, or Quinton de Kock, or Hashim Amla, or JP Duminy. Perhaps even Dean Elgar or Temba Bavuma, who have shown form in this series. If they were listening to the TV commentary, they may even have said Kevin Pietersen. As for Stephen Cook, nothing in the past month suggested he would be even a minor irritant.
But it was Cook who did most to hold the Australians off, and by the close of play he was on 81 and Quinton de Kock was yet to score, with the total sitting at 6 for 194. Cook entered this Test with tour scores of 5, 12, 0, 0, 12, 23 and 11 - and remember that four of those scores came against sub first-class opposition in warm-up games. The only South African who had played both Tests and scored less runs than Cook this series was Kagiso Rabada.
However, in the first innings Cook found a way to grind out 40, and in the second he managed his first fifty of the trip. It was not easy, nor pretty. At times it was downright ugly, and the Adelaideans who chose to spend their Saturday night in the cold, watching Cook bat, might have wondered at the wisdom of their choice. And yet it was gripping Test cricket; Australia's attack were baying, yet being kept at bay by a batsman who had so recently been all at sea.
Cook knows a thing or two about patience - he owns the fifth-longest first-class innings of all time, an 838-minute effort that brought him 390 runs in 648 balls. Here, he worked many of his runs through the leg side when Australia's bowlers got too straight. Only two of his seven boundaries came through the off side - and both of those were edges through a gap in the cordon. All that mattered to South Africa was that he was still there.
Wickets fell around him. In the first over of the innings, Elgar edged Starc to slip and was caught for a third-ball duck. Amla, put down on 13 when wicketkeeper Matthew Wade and first slip Matt Renshaw both failed to move quickly enough to claim an edge off Starc, was eventually caught behind off Hazlewood for 45. It meant that in every innings of the series, Amla had fallen to the bowling of Hazlewood.
JP Duminy fell to an uncharacteristically poor shot when he played across the line trying to work Lyon to leg, and was bowled for 26 from 70 balls. Starc, who sent down some searing bouncers and seemed to be back at his best, had du Plessis snapped up sharply by Peter Handscomb at gully for 12.
Temba Bavuma, who had valiantly and repeatedly tried to hook Starc, eventually fell to the spin of Lyon for 21 when he top-edged a sweep and was caught by Smith, running behind the wicketkeeper from slip. And Lyon claimed his third when nightwatchman Kyle Abbott played back and was lbw for a five-ball duck, narrowly failing to do his job of keeping de Kock safely inside for the evening.
The day had begun with Australia on 6 for 307, and they added 76 to their overnight score for the loss of their final four wickets. Usman Khawaja, who had been batting since the first evening, was lbw to Vernon Philander for 145, his 308-ball innings the longest by an Australian opener in a home Test since Justin Langer made a double-century at Adelaide Oval in 2004.
But even after Khawaja departed, the Australia tail provided some frustrations for du Plessis and his men. Starc struck five fours and one six on his way to 53, which was the seventh half-century of his Test career, before he prodded a return catch back to Rabada, who finished with 3 for 84.
The debutant left-arm wrist-spinner Tabraiz Shamsi endured a long wait for his maiden Test wicket but finally achieved the feat in his 27th over when he had Lyon caught top-edging a sweep for 13. Hazlewood finished unbeaten on 11 when the final wicket fell, Bird caught at slip off Rabada for 6.
It meant Australia had been dismissed for 383, their highest Test total since the tour of New Zealand in February, and held a first-innings lead of 124. And despite the fight of Cook later in the day, Australia went to stumps with a good chance of avoiding being on the wrong end of a historic home whitewash.

Brydon Coverdale is an assistant editor at ESPNcricinfo. @brydoncoverdale