The third test decider is delicately poised after South Africa closed day three on 140-4, leading Australia by just 40 runs at Newlands on Thursday.

Temba Bavuma, 35, and Matthew Breetzke, 19 not out, had fought to steady the innings before Nathan Lyon, 1-31, bowled the Proteas captain five minutes before stumps, after he passed 4000 test runs.

Australia had started the day on 300-4, leading by one, with Josh Inglis, 102, and Alex Carey, 80, extending their partnership to 191.

Inglis reached his second test ton before Harmer had him caught, then removed Carey at slip.

The Proteas roared back after lunch, taking the last six wickets for just 59 runs to bowl Australia out for 429, with a lead of 100.

Harmer finished with 4-104 and Marco Jansen 3-60, while Gerald Coetzee, Kagiso Rabada and Wiaan Mulder all chipped in, too.

South Africa’s second innings wobbled immediately as Mitchell Starc, 2-29, removed Aiden Markram for one and Josh Hazlewood dismissed David Bedingham for 11.

Marques Ackerman made 62 before gloving Starc to slip, leaving Breetzke and Ryan Rickelton not out to see out Thursday and set up a fascinating penultimate day’s play.