Usman Khawaja was five runs short of a maiden double-century when play was abandoned on day two of the third test against South Africa on Thursday, with Australia in complete command at 475 for four.

Khawaja was on a career-high score of 195 not out, with Matt Renshaw coming out of his COVID-19 segregation to be unbeaten on five when a shower stopped the resumption after the drinks break at the Sydney Cricket Ground.

After Steve Smith scored his 30th test ton before tea, Travis Head hammered a Twenty20-style 70 from 59 balls after the break before holing out in the deep, with South Africa's hopes of a face-saving win fading through the day.

The match is a dead rubber after Australia sealed the series with wins in Melbourne and Brisbane, but Pat Cummins's side can book their place in the World Test Championship final with another victory.

Smith joined a group of 14 cricketers with his 30th test ton before spinner Keshav Maharaj had the number four caught and bowled for 104, ending a 209-run partnership with opener Khawaja.

Pakistan-born Khawaja earlier collected his 13th test ton to continue his love affair with the SCG, which is just down the road from the two-bed flat he grew up in.

The 36-year-old Queensland captain reignited his international career in last year's New Year's test at the venue, scoring twin Ashes hundreds against England.

Nearly an hour into the second session, Khawaja, on 119, cut Rabada straight to point where a startled Anrich Nortje misjudged the flight of the ball.

It brushed past his leg on the way to the fence, leaving Rabada fuming.

Khawaja struck three fours off Rabada in the next over, with two edges racing between the lone slip and gully.

Teaming up with Smith to attack Maharaj, Khawaja drove a half-volley off the spinner through the covers to bring up his 150 on the 305th ball.

Moments later Smith pulled Nortje for four to bring up his century but he was out soon after, spooning a simple catch to Maharaj.

Khawaja, the third-highest scorer in 2022 with 1,080 runs in tests, had earlier raised his own century with a pull-shot off Rabada and a mad scramble for two runs.

With his beaming wife cradling his two small daughters in the terraces, Khawaja celebrated with a David Warner-style leap and a punch in the air, then danced a little jig with his helmet off.