The visitors went into the interval at 84/3, but Smith fell for 25 in the first over after the break, caught by Mulder off Jansen to leave the visitors 84/4.
Renshaw and Alex Carey tried to rebuild, adding 36 for the fifth wicket before Anrich Nortje struck twice in two deliveries.
Carey was caught by Aiden Markram for 14, then Beau Webster edged behind for four, leaving Australia struggling at 124/6.
The visitors were 149/6 at tea after 53 overs, with Renshaw unbeaten on 32 and Cummins on nine as SA's seamers took two wickets each to keep the scoring rate in check.
The final session brought a change in momentum as Renshaw and Cummins dug in, frustrating the hosts. Renshaw reached an unbeaten 46 from 115 balls, while Cummins made 33 not out from 72, striking five fours.
Their stand passed 50 and reached 63 from 140 deliveries, taking Australia to 187/6 after 65.2 overs, adding 38 runs without loss after tea, ensuring SA could not finish off the innings before the weather intervened.
Play was halted by bad light, with conditions steadily deteriorating before stumps were drawn shortly before 4pm.
Australia will resume on the second morning at 9.30am with Renshaw and Cummins at the crease, while Mitchell Starc, Nathan Lyon and Josh Hazlewood to come.
Mulder finished with 2/31, Jansen 2/35 and Nortje 2/40, leaving the hosts in control but with work still to do.