The visitors reached stumps on 330-4 after 90 overs, leading by one run, as Josh Inglis and Alex Carey frustrated the Proteas with an unbeaten 145-run fifth-wicket partnership.

South Africa had threatened to take charge when Jansen struck twice shortly before tea, removing Matt Renshaw (74) and Cameron Green (65) to reduce Australia to 185-4.

However, Inglis and Carey survived the remainder of the afternoon before batting through the final session to give Australia the advantage heading into day three.

Earlier, Harmer made an immediate impact after the Australian openers had put on 58.

The off-spinner bowled Travis Head for 41 with his first delivery before having Marnus Labuschagne caught by Aiden Markram at slip for a duck off the final ball of the same over.

Australia reached lunch on 90-2, with Renshaw and Green then frustrating the hosts during the afternoon session.

Both batsmen brought up their half-centuries before Jansen provided the breakthrough South Africa desperately needed.

The left-arm quick had Renshaw caught behind by Ryan Rickelton to claim his 100th Test wicket in just his 24th match.

Jansen struck again soon afterwards when Green edged to Harmer at slip, leaving Australia on 185-4.

The Proteas went to tea with Australia on 191-4, still trailing by 138 runs, but failed to build on their momentum after the interval.

Inglis and Carey batted patiently against the South African attack, with Kagiso Rabada, Gerald Coetzee and Wiaan Mulder unable to find the breakthrough.

Their partnership ensured Australia finished the day with six first-innings wickets in hand.

South Africa had posted 329 on the opening day, with Marques Ackerman top-scoring with 95 and Aiden Markram contributing 78 before Mitchell Starc claimed 6-72.

The Proteas will need early wickets on day three to prevent Australia from establishing a significant first-innings lead.

The three-match series is level at 1-1 after Australia won the opening Test in Durban before South Africa responded with an innings-and-31-run victory in Gqeberha.

Photo: Grant Pitcher/Gallo Images