Dale Steyn may have the deciding say in the Wanderers Test, with both bat and ball. His cameo of 41 off 64 balls pushed South Africa's lead past 300, and with the pitch remaining seamer-friendly, Hashim Amla expects that swing will play a key role in South Africa's quest to bowl Australia out on the final day.

"A lot of wickets have fallen with the older ball rather than the newer ball, and the ball was moving around a bit," Amla said. "In Johannesburg it tends to swing more than at the coast." With Australia fast bowler Pat Cummins saying "it swung for us for the 90 overs", Steyn's ability is set to come into play dramatically.

He has found good rhythm in the Test and took 4 for 64 in the first innings, denied a five-for only through a dropped catch. On the fourth day, Steyn did not get a wicket and varied his lengths with little success, but he has shown himself to be a bowler that gets better in later spells.

Rain is still expected but has yet to fall, leaving the air heaving with moisture and setting Steyn up for a match-changing spell, which Amla says has to begin early. "The morning sessions are crucial," he said. "You have to hope you play good lines and try to score off the bad balls."

Although bowlers on both sides have struggled with consistency, Amla said that there is still enough in the pitch for them to make batting difficult. "It's not an easy wicket to bat on. There are certain times in the game when it seems to be doing a little bit more than usual. If you string a good few overs together, there is a bit of movement off the seam through the air."

A target of over 300 has never been successfully chased at the Wanderers before, with the highest winning-score achieved there being 292, by Australia in 2006. Setting the visitors a challenge that would surpass that record mark gave South Africa a psychological edge, according to Amla. "Chasing over 300 is always daunting," Amla said. "Steyn's innings gave us momentum at the backend."

As Steyn showed, batsmen are equally capable of succeeding on this pitch, provided they approach their task with the man at the other end on their mind. "If the batters get a partnership going, they can score quickly," Amla said.

Australia would have the advantage of a set pairing had Usman Khawaja not been dismissed at the stroke of stumps. He shared a 122-run partnership with Ricky Ponting and showed exquisite technique, especially in his judgement of when to leave the ball, before Imran Tahir had him caught at slip. "Getting a wicket so late in the day was a big boost for us," Amla said. "If we pick up an early wicket tomorrow morning, it will put a lot of pressure on them. You'd rather be in our change-room than in theirs."

The players left the field at 17.05, 25 minutes before the scheduled close. It was not quite all that dark yet, and the decision was thought to be premature. Amla said South Africa could have benefitted from more time in the middle, but will not dwell on the lost time. "The fact that we had just got a wicket might have given us some motivation to keep going but these things are out of our control," he said. "We just do as we are told."