Usman Khawaja and Steve Smith scored centuries as Australia built a massive lead before rain intervened again on the second day of the third Test against South Africa at the SCG on Thursday.

Australia were 475-4 at stumps after play was interrupted by light rain at drinks in the final session with Khawaja unbeaten on 195* alongside Matt Renshaw (5*).

The hosts were utterly dominant, beating the Proteas into submission, with only two wickets falling across 84 overs bowled for the day. However, the issue of time remaining in the Test looms large after more delays on day two, with grim weather forecast for Sydney in the coming days.

Khawaja had resumed alongside Smith with Australia 148-2 after only 47 overs were bowled on day one due to a combination of bad light and rain.

After an early rain delay, the 36-year-old left-handed opening batsman led from the front, bringing up his 13th Test century late in the opening session with two off Kagiso Rabada.

Khawaja celebrated his third straight SCG hundred with an air-punch and a little jig. Smith brought up his half-century shortly after.

South Africa skipper Dean Elgar demonstrably discarded the old ball when the Proteas took the new ball shortly before lunch, but it led to few opportunities for the tourists.

Smith went on to bring up his 30th Test century, surpassing the great Sir Donald Bradman, pulling to the backward square leg boundary from Anrich Nortje to reach triple figures.

But the vice-captain was dismissed caught and behind by Keshav Maharaj for 104 in the next over, ending their 209-run third-wicket stand. That marked the pair's 10th century partnership from 33 innings.

Travis Head kept the game moving with aggressive stroke play, blasting eight fours and one six before being caught by sub fielder Rassie van der Dussen at deep square off the tiring Rabada.

Renshaw, who tested positive to COVID on day one and had to keep his distance from team-mates, batted late in the day before stumps was called.

Patient Khawaja bats through

Khawaja finished the day unbeaten on 195, having faced 368 deliveries with 19 fours and one six, batting through the opening two days, albeit amid numerous delays. The Queenslander's 195* is his highest Test score and he will be chasing a maiden Test double hundred on Friday.

Maharaj breaks duck

Proteas left-arm orthodox spinner Maharaj had endured a lean series prior to claiming Smith's wicket, which was his first in the three Tests. That dismissal ended Maharaj's dire record of 0-247 from 66.5 overs in the series.