Nortje injury scare clouds Australia's stuttering reply in Gqeberha

Australia continued to labour against South Africa's attack on the fourth morning at St George's Park, reaching 56-4 with Steve Smith stuck on 17 for several overs and Matt Renshaw grinding out singles, according to the Guardian's live coverage of the Test.

Simon Harmer bowled long, tight spells to keep the pressure on, with the Guardian's blog noting he could remain locked in at one end for much of the day.

South Africa's attack suffered a blow when Lungi Nortje walked off during the 20th over after bowling, then stopping to stretch out his ankle and calf. He was later shown in the dressing room with an ice pack on his thigh, the Guardian reported, leaving Harmer to complete the over in his absence.

The loss of Nortje for any length of time would be a significant setback, with the Guardian's coverage pointing out it would be much harder for South Africa to enforce a follow-on, set at 225, while already a bowler light.

Australia's four wickets in the innings had come in varied fashion rather than through the wobble-seam bowling that troubled them earlier in the series, with the Guardian's live blog describing Nathan Maddinson's dismissal as a poor drive, Scott Boland as reaching for a delivery, Travis Head as undone by conventional nip, and Marnus Labuschagne as playing the wrong line.

The tourists' fragile position follows a dramatic third day in which South Africa, having slumped to 97-5 overnight and then 110-6, were rescued by an unbroken stand between captain Temba Bavuma and Marco Jansen, according to Yahoo Sports.

The pair added 106 runs in 22 overs to take South Africa to 216-6 at lunch, breaking the previous record seventh-wicket partnership at St George's Park, a mark that had stood since 1896.

Bavuma had reached 43 when Jansen arrived at the crease, and the all-rounder had all but caught his captain by the interval, reaching fifty off 43 balls after striking sixes off Boland, Pat Cummins and Renshaw and surviving an lbw appeal from Renshaw on 58, Yahoo Sports reported.

By lunch, Bavuma was unbeaten on 76 from 189 balls and Jansen on 72 from 71, having opened his innings by taking three boundaries off Mitchell Starc and two more off Boland.

Starc had struck earlier in the day, removing Wiaan Mulder when a 144kph bouncer clipped his glove and was caught at slip, the delivery bringing up the bowler's 450th Test wicket, Yahoo Sports noted.

Josh Hazlewood, who missed time off the field through illness on the Monday, was due to return to the attack with the new ball not long after lunch on day three, having made up the overs he had been unable to bowl.

With Nortje's participation now in doubt and Australia still four wickets shy of parity with a bowler down on South Africa's side too, the shape of the rest of the Test at St George's Park is likely to hinge on how much bowling the hosts can extract from their remaining attack through the rest of day four.