Port Elizabeth - With a lead of 369 after three days, South African fast bowler Morne Morkel says his side could declare after the morning session on day four.
AS IT HAPPENED: SA v Australia - Day 3
South Africa reached 192/4, with Hashim Amla (93 not out) and Quinton de Kock (nine not out) in the second Test at St George's Park in Port Elizabeth on Saturday.
"We'll see after the first session tomorrow and assess where we are," Morkel said at the close of play.
"450 always seems to be the magical number with declarations."
Bad weather was predicted for day five of the Test on Monday, but Morkel said his side had little faith in weather predictions.
"Of late you can't really trust the weather, right now we've got two guys at the wicket who can score fast."
Australian captain Michael Clarke, meanwhile, suggested he may have declared already were he in South Africa's position.
"I would have had five overs at them tonight if I were them," said Clarke.
Faced with an uphill battle for the remainder of the Test, Clarke was optimistic.
"We're behind in the game, that doesn't mean the game is over.
"We'll need to bat our backsides off to get there, and you never know in this game. That's for sure."
The Proteas bowled out the visitors for 246 earlier in the day.
Amla, who batted for 126 balls and struck 12 fours, came in to bat at his regular position of number three, after he dislocated his left ring finger while fielding in the morning session.
Together with Faf du Plessis (24), Amla shared in a quickfire 70 run third wicket partnership off just 83 balls.
Du Plessis was out as he edged a rising delivery from Peter Siddle (2/53) through to Brad Haddin as South Africa lost their third wicket on 112.
AB de Villiers was removed by Mitchell Johnson for 29 late in the day, as the hosts attempted to maintain their quick run rate of 4.5 runs per over.
Amla, however, was given a chance in his knock. On 83, he edged a Mitchell Johnson delivery down the legside, and Brad Haddin put down the catch.
Amla was unbeaten at the crease at the close of play, with debutant Quinton de Kock (9) at the other end.
When South Africa came into bat after lunch, Graeme Smith got an inside edge off a Johnson delivery, and the ball cannoned into his leg stump as he left the scene for 14.
Dean Elgar made 16 before he was out caught Haddin off the bowling of Siddle, as South Africa fell to 42 for two.
Earlier in the session, South Africa bowled out Australia for 246.
Vernon Philander (3/68) and Morne Morkel (3/63) both returned good figures as the hosts achieved a 177 run first innings lead.
Steve Smith made 49, before falling to Morkel. David Warner was top scorer for Australia with 70, but was out slashing at a Philander delivery outside off, caught Smith at first slip.
South Africa started the day by claiming for wickets in the morning session.
It was not all good news for South Africa though, as both Amla and Wayne Parnell went off the field with injuries during the session.
Fielding at gully, Amla dived for a catch off Haddin in the 32nd over, but only managed to get the finger on it. Amla immediately went off the field, and had 'the finger put back in' according to team management.
In the 40th over of the innings, Parnell was forced to leave the field in the middle of his ninth over with a groin strain. Parnell had bowled three balls in the over when he pulled up in his run up with the injury.
It was later revealed he would be unable to bowl again in the Test.