South Africa's bold attempt to win the third and final Test against Australia was almost certainly ruined by persistent rain on Thursday.

Less than 21 overs were completed on a gloomy fourth day at the Sydney Cricket Ground, effectively thwarting the visitor's hopes of salvaging a drawn series.

The tourists, needing a win to square the series after drawing in Perth then losing in Melbourne, ended the day leading by 186 runs with seven second-innings wickets in hand.

They had been frantically trying to build a bigger lead and make an early declaration before trying to bowl the Australians out on the last day, but now face the prospect of a draw with more foul weather forecast for Friday.

Thursday's start of play was delayed by an hour because of morning showers and less than six overs were bowled after lunch when the heavens opened up again.

Herschelle Gibbs [Images] had led South Africa's charge with an exhilarating 67 off 74 balls but ran himself out in the pursuit of quick runs.

Playing a virtual lone hand, Gibbs pounded 11 boundaries in his 98-minute innings before he was caught short of his ground by a direct-hit from Brad Hodge after a mix-up with Jacques Kallis [Images].

Kallis was unbeaten on 14 at the close with Ashwell Prince yet to score. Kallis and Prince both scored first-innings centuries in a record fourth-wicket partnership of 219 that took more than six hours when the tourists employed a go-slow policy over the first two days.

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South Africa had started the fourth day on 4-1 but lost captain Graeme Smith [Images] for five with the total on six when he was trapped lbw by Glenn McGrath.

Smith turned down the chance to go off for bad light but was given little reward for his initiative when he was given out to a ball that struck him high above the knee roll and looked to be sailing over the top of the stumps.

Unperturbed by Smith's dismissal and a damp outfield, Gibbs launched into the Australian bowlers with renewed vigour while Kallis, hampered by an elbow injury that forced him to miss the drawn first Test, was content to play the anchorman.

Gibbs had a let-off on 34 when he was dropped by Shane Warne [Images] at slip but raced to his second half-century of the series off 58 balls in 73 minutes when he dispatched McGrath to the rope.

McGrath's frustration boiled over when Gibbs was dropped and the Australian paceman was later reported by the on-field umpires Aleem Dar and Billy Bowden and third umpire Bob Parry for offensive behaviour.

Scorecard:

South Africa  1st innings  451 for 9 decl  (A. Prince 119, J. Kallis 111)
Australia 1st innings  359 (R. Ponting 120, A. Gilchrist 86; A. Nel 4-81)

South Africa 2nd innings (Overnight: 4-1)
G. Smith        lbw b McGrath               5
A. de Villiers  lbw b Lee                   1
H. Gibbs        run out                    67
J. Kallis       not out                    14
A. Prince       not out                     0
Extras          (b-2 lb-2 nb-2 w-1)         7
Total           (for 3 wickets, 22 overs)  94

Fall of wickets: 1-4, 2-6, 3-92

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