Allegations of ball-tampering against Cameron Bancroft are certain to dominate the headlines after day three of the third Test between South Africa and Australia in Cape Town.

The Proteas moved into a commanding position on Saturday as they opened up a 294-run lead, reaching 238-5 in their second innings after finishing off the tourists for 255.

But it is the Bancroft incident that provided the biggest talking point.

The Australia opener, who hit 77 on Friday, was seen to rub the ball with a foreign object, which he then returned to his pocket before dropping it down the front of his trousers.

Bancroft produced a black sunglasses carrier when pressed over the incident by the umpires, appearing to imply that the case was the only item in his pocket.

Spectators speculated on social media that the item used and then swiftly hidden by Bancroft was sandpaper, although there is no concrete evidence to confirm whether this was the case.

The match continued with no further action taken, but Bancroft is likely to face questions over the incident.

Australia could only add 10 more to their overnight total before Kagiso Rabada took the final wicket of Josh Hazlewood (10).

Aiden Markram - having been dismissed for a duck in the first innings - was a pillar of strength for the hosts early in the second, racking up 84 runs after surviving tough dropped chances by Usman Khawaja and Steve Smith when he was on 0 and 59.

Dean Elgar, who carried his bat first time round, was unable to replicate his heroics as he fell for 14 but AB de Villiers picked up the baton from Markram to finish unbeaten on 51, with Quinton de Kock (29 not out) also returning to bat on Sunday, after play was stopped by bad light.

The Bancroft incident is the latest in a string of controversial moments that have blighted this four-match series, which is tied at 1-1 after two Tests.

David Warner was in the headlines during the first Test in Durban after becoming involved in a heated exchange with De Kock as the teams left the field for tea on day four.

It was alleged the wicketkeeper had made personal comments regarding Warner's wife and the ICC fined and handed demerit points to both men.

In the second Test in Port Elizabeth, Rabada risked disciplinary action by brushing shoulders with Smith having dismissed the Australia captain.

Rabada was initially suspended for two games - the remainder of the series - but managed to overturn that decision on appeal.

Warner then appeared to become embroiled in a verbal spat with a spectator on day two of this Test as he left the field after being clean bowled by Rabada.

Faf du Plessis, who hit 20 on Saturday, was found guilty of ball-tampering during a 2016 series between the two sides, when he applied saliva to the ball with a sweet in his mouth.

The South Africa skipper was fined his full match fee and given three demerit points over the incident.