South Africa's AB de Villiers (left) and Faf du Plessis adjust their helmets while batting together at the Adelaide cricket ground during the fourth day's play of their second cricket Test match in Adelaide.

Adelaide - AB de Villiers and Faf du Plessis boosted South Africa's hopes of securing a draw in the second Test against Australia, protecting their wickets for two hours in draining heat to guide their side to 126 for four at lunch on the fifth and final day on Monday.

Resuming on 77-4 after having batted out most of the final session on Sunday, wicketkeeper De Villiers and debutant Du Plessis proved unyielding to both spin and pace bowling, and left the hosts frustrated at the lunch break.

De Villiers was on 31 and Du Plessis, who survived two lbw appeals on review, was on 49, their team still 304 runs behind a victory target of 430 set by Michael Clarke following his declaration after lunch on day four.

All thoughts of a South African victory were banished shortly after tea on Sunday, when Australia's bowlers rattled through the tourists' top order to leave them reeling at 45-4.

De Villiers and Du Plessis were primed for the task of playing out a gritty draw, however, and despite being swarmed by fielders around the crease, stubbornly padded up time and again to offspinner Nathan Lyon and part-timer Clarke.

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 over-turned 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. - Reuters