South Africa doggedly batted out the final day to draw the second Test against Australia in Adelaide and leave the three-Test series all square on Monday.
Allrounder Du Plessis, playing in his debut Test, was the hero with an unbeaten century as the Proteas finished on 248 for eight ahead of Friday's final Test in Perth.
When stumps were drawn, Du Plessis, who needed physio treatment for cramp late in the day, was unconquered on 110 with Morné Morkel not out eight.
The Australians need to win the three-Test series against the Proteas to take the world No. 1 ranking from South Africa.
It was the second time the South Africans had batted out for a draw after denying Australia's unlikely victory push in the Brisbane opener earlier this month.
Du Plessis, on his debut, was on 94 from 277 balls at tea on the fifth and final day, with the injured Jacques Kallis on 38.
The pair stood firm after paceman Peter Siddle captured South Africa's fifth wicket shortly after lunch on a day of stifling heat at Adelaide Oval.
Du Plessis and all-rounder Kallis pushed South Africa to 212-5 at the break, but their partnership remains the last bulwark between Australia's bowlers and the tail-end.
Australia were demoralised by a dropped catch by Matthew Wade in the second-last ball before the break, when paceman Ben Hilfenhaus had Du Plessis nick to the wicketkeeper.
South Africa remain 218 runs shy of victory but will feel they have a good chance to save the Test with Australia's attack tiring in the heat and without the support of paceman James Pattinson.
Despite the hot and muggy conditions, fiery paceman Siddle kept steaming in and was rewarded by bowling AB de Villiers in his second over after lunch.
Having moved his previous deliveries away from the wicketkeeper, Siddle bowled a stinging off-cutter through the gate to remove the wicketkeeper for 33 and end the fifth wicket-partnership after a marathon 68 overs.
De Villiers's wicket briefly perked up the Australian bowlers, who had toiled fruitlessly for the whole morning session.
Three overs later, Kallis was nearly on his way back to the dressing room for six after he miscued a drive that fired back toward the bowler, Nathan Lyon.
Lunging high and to his right, Lyon got one hand to the ball but put the tough chance down.
Kallis and Du Plessis combined for a morale-boosting eighth-wicket stand of 93 in the first innings to help South Africa avoid the follow-on, and duly re-built their wall of resistance after lunch, seeing off every specialist and part-time bowler skipped Michael Clarke could throw at them.
Du Plessis celebrated his second half-century this Test in unnerving fashion, slashing at a wide delivery off Hilfenhaus that flew through the air wide of the lunging gully on the fourth bowl after lunch.
Kallis, scoring slightly freer than his counterpart, punched five boundaries and was a picture of serenity as he trotted between the wickets to protect his strained hamstring.
Resuming on 77-4 after having batted out most of the final session on Sunday, De Villiers and Du Plessis had no thoughts of pursuing victory after Australia rattled through the top order to leave South Africa 45-4 shortly after tea on day four.
Australia were frustrated twice by referral decisions, after Clarke had Du Plessis trapped in front immediately before and after the drinks break.
Both were given out and both decisions overturned on video review by the batsman.
The first review showed the ball pitching slightly outside leg stump before cannoning into Du Plessis's pad, while the second showed the ball had never touched any part of the all-rounder's leg and had actually deflected off his bat.
Seemingly out of desperation, Clarke demanded a video review of another lbw decision against Du Plessis off Lyon's bowling immediately before lunch, but the review showed the ball flying over the stumps.
The three-Test series hangs in the balance after the drawn first Test in Brisbane, with the final match to be played in Perth later this week. – Sapa, Reuters