Ricky Ponting scored a brilliant century in his 100th Test to lead an Australian fightback in the final Test against South Africa on Wednesday.

The Australian skipper slammed 120 before Adam Gilchrist returned to form with a swashbuckling 86 to help the world champions finish on a respectable total of 359 after they started the day in deep trouble at 54-3.

South Africa led by 92 on the first innings after declaring at 451 for nine the previous day and stretched their advantage to 96 by close of play on day three but lost a wicket in the process.

AB de Villiers was trapped lbw by Australia's express paceman Brett Lee on what was the last ball of the day, leaving South African captain Graeme Smith unbeaten on three and his team 4-1 in their second innings with two days to go at the Sydney Cricket Ground.

The tourists might have had a much bigger lead had it not been for Ponting and Gilchrist who tore into the visiting bowlers with a ferocity that belied Australia's shaky position.

Ponting joined Colin Cowdrey, Javed Miandad, Gordon Greenidge, Alec Stewart and Inzamam-ul-Haq as the only players to reach triple figures in their 100th Test with a cavalier display.

The Australian skipper resumed on 13 after the first hour was washed out by rain but quickly made up for lost time, chalking up his 27th Test hundred after lunch in 215 minutes from 143 balls.

The 31-year-old, who made 96 on his Test debut against Sri Lanka a decade ago, hit 12 boundaries and a six as well as sharing a fourth-wicket partnership of 130 with Hussey that laid the platform for Australia's fightback.

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They batted through the rain-shortened morning session before Hussey was caught by wicketkeeper Mark Boucher off debutant spinner Johan Botha then Ponting was trapped lbw by Jacques Kallis just before tea.

Ponting's dismissal triggered a minor collapse with Andrew Symonds (12) and Shane Warne (no score) falling in successive deliveries off Andre Nel to leave Australia struggling at 226-7 at tea, still 26 short of avoiding the follow-on.

But Gilchrist, who had been struggling since the Ashes, rediscovered his form to keep the tail wagging, belting 10 fours and two sixes off 109 balls in 156 minutes.

Gilchrist initially preferred to take singles while shielding the tailenders from the strike, but grew in confidence.

He shared a 37-run partnership with Lee (17) to steer Australia past the follow-on point, then a 59-run stand with Stuart MacGill (29) and another 37-run partnership with Glenn McGrath (one not out).

Nel was the pick of the South African bowlers, finishing with 4-81, while Kallis and Charl Langeveldt captured two wickets each. South Africa need to win the match to square the series.

Scorecard:

South Africa 1st innings  451 for 9 decl  (A. Prince 119, J. Kallis 111)

Australia 1st innings (Overnight: 54-3)
J. Langer       b Langeveldt                 25
M. Hayden       b Langeveldt                  4
R. Ponting      lbw b Kallis                120
B. Hodge        c Rudolph b Nel               6
M. Hussey       c Boucher b Botha            45
A. Symonds      lbw b Nel                    12
A. Gilchrist    c Boucher b Nel              86
S. Warne        c Boucher b Nel               0
B. Lee          c Smith b Kallis             17
S. MacGill      c Nel b Pollock              29
G. McGrath      not out                       1
Extras          (lb-10 nb-2 w-2)             14
Total           (all out, 95.1 overs)       359

Fall of wickets: 1-22, 2-35, 3-54, 4-184, 5-222, 6-226, 7-226, 8-263, 9-322, 10-359

Bowling
S. Pollock      25 - 3 - 109 - 1 (nb-2)       
C. Langeveldt   24 - 4 - 108 - 2 (w-1)        
A. Nel          24.1 - 3 - 81 - 4             
J. Kallis       15 - 4 - 25 - 2 (w-1)         
J. Botha        7 - 2 - 26 - 1                

South Africa 2nd innings
G. Smith        not out                       3
A. de Villiers  lbw b Lee                     1
Total           (for 1 wickets, 1.3 overs)    4

Fall of wickets: 1-4

To bat: H. Gibbs, J. Kallis, A. Prince, J. Rudolph, M. Boucher, S. Pollock, C. Langeveldt, A. Nel, J. Botha

Bowling                                    
G. McGrath      1 - 0 - 4 - 0                 
B. Lee          0.3 - 0 - 0 - 1