Usman Khawaja made his highest Test score, Steve Smith scored a milestone century and Australia reached a commanding 475-4 when rain forced an early end to the second day of the third and final Test against South Africa. (More Cricket News)

Khawaja made an unbeaten 195 off 368 balls, with 19 boundaries and a six, and had earlier Thursday shared an epic 209-run partnership with Steve Smith, who made his 30th Test century and also became Australia fourth-highest run scorer in tests in front of his home Sydney Cricket Ground fans.

Marnus Labuschagne (79) and Travis Head (70) both scored half-centuries as Australia dominated a placid South Africa attack and placed themselves in a strong position to still force a result in a game that has had frequent bad light and rain delays.?

Khawaja raised his third consecutive SCG hundred before lunch Thursday and then pushed past his previous highest test score of 174 — against New Zealand at Brisbane in 2015 — to close in on his maiden double-century.?

Khawaja was given a life on 119 when he offered a sharp shin-height chance which Anrich Nortje missed at gully after losing sight of the ball.?

Earlier, Smith made 104 to join former Australia opening batter Matt Hayden on 30 test centuries. Only Ricky Ponting (41) and Steve Waugh (32) have more among Australian men's test players.?

It was Smith's fourth century at his home ground and came from 190 balls, with 11 boundaries and two sixes with the former captain receiving a prolonged standing ovation from the 27,663 SCG crowd.

Next over Smith chipped a simple return catch to Keshav Maharaj (1-108) in what was the only blemish in an otherwise flawless four-hour innings.?

On the way to his latest ton Smith passed Hayden (8,625 runs) and Michael Clarke (8,643) for career runs and is now the fourth-highest Australian test run scorer with 8,647 runs, behind Ponting (13,378), Allan Border (11,174) and Waugh (10,927). Smith averages over 60 runs an innings across his 92 Tests.

After twin centuries in a triumphant return to test cricket against England last year, Khawaja had earlier completed his 13th hundred off 206 balls, with nine boundaries as he and Smith serenely accumulated runs after resuming the day at 147-2.

Khawaja made 137 and 101 not out against England in the Test here last year to firmly re-establish himself in Australia's batting lineup after being dropped during the 2019 Ashes series.?

Khawaja and Head combined for a brisk 112 run partnership before Head holed out in the deep off Rabada (1-119).?

Shortly after play commenced Wednesday, Australia team management advised that batter Matt Renshaw — in the team for the injured Cameron Green — had reported feeling unwell shortly before the match and had subsequently returned a positive test for COVID-19 but would still take part in the match.

Matt Renshaw, in his first test since 2018, was separated from the remainder of his teammates and moved into another changing room at the SCG. He batted as expected at No. 6 and was five not out at the end of the day's play.

International Cricket Council regulations state Renshaw is permitted to play in the match as long he feels well enough, with the option for a like-for-like substitute if he was unable to play.

Australia has already won the series after two crushing defeats in the first two Tests at Brisbane and Melbourne.?

A win for Australia in this third Test would confirm its place in the World Test Championship final to be played at Lord's in England in June this year.