In a big-stage reprisal of so many boyhood backyard matches, brothers Shaun and Mitchell Marsh took the sword to a dispirited England late today as the final Magellan Ashes Test slipped further from the tourists' grasp.

After Usman Khawaja dominated the first two sessions to post his maiden Ashes century and come within an elegant boundary of his highest Test score, the brothers Marsh took to a tiring England attack in a brutal fifth-wicket stand that will resume tomorrow having already yielded 104.

At a rate hitherto unseen in this match, the siblings' century stand arriving from 151 balls as older brother Shaun ended the day within two runs of his second hundred of the series and the pair relived their days playing pretend Ashes Tests on their family's lawn tennis court in Perth.

As a consequence, Australia will head into day four on which Sydney temperatures are forecast to climb past 40C at 4-479 with a lead of 133 and England's bowlers already having spent 10 hours and 44 minutes in the field at the end of a winless Test campaign to date.

The small solace England can extract from another soul-destroying day is that they denied Australia's inexhaustible run robot Steve Smith from a century that would have seen him take a place alongside his nation's foremost player Don Bradman with four tons in a single Ashes series.

When Smith was dismissed for 83, sending a soft return catch to Moeen Ali to become the spinner's fourth wicket in almost five Tests, England remained 72 runs ahead and with game notionally in the balance.more details....