A mentally broken England will need to produce a minor miracle if they're to avoid an unwanted place in history, with Australia going to stumps at 4-140 already holding a commanding lead of 311.
England suffered the second worst collapse of an already disastrous series to be all out for 155 at tea, surrendering a 171-run deficit.
Ryan Harris (3-36) and Mitchell Johnson (3-33) delivered a devastating opening spell, before Peter Siddle (3-23) did the rest.
The highest successful fourth-innings chase at the SCG was Australia's 2-288 against South Africa in 2006.
But if Chris Rogers (73 not out) can make his second ton of the series and George Bailey (20no) can produce a career-saving knock, Australia will be hoping to press into world record territory by setting a target of 400 plus.
Australia suffered another worrying top order slide of their own to lose 4-91 in the final session, but not for the first time this series, their failings are unlikely to matter thanks to the form of the bowlers and the incompetence of England's batsmen.
Thirteen wickets fell on an action-packed day two, after England resumed on 1-8.
After 70 deliveries they were in complete disarray having lost a further four wickets for just 17 runs to be 5-23.
At that point chief executives from Cricket Australia, the SCG and the McGrath Foundation might have been tearing their hair out at the prospect of a two-day Test.
England crawled their way past 127 runs to avoid the follow on, but it seems only a matter of time until the third 5-0 clean-sweep in Ashes history is secured.
Only two England batsmen made it out of the teens, Stuart Broad (30 not out) and impressive allrounder Ben Stokes, who was bowled by Siddle for a top score of 47.
England's top five batsmen produced a top score of 7 - an all-time low - with six players recording single-figure scores.
Nathan Lyon took a wicket, but once again the fireworks came from a pace-attack that's survived unchanged through the series and been described by Glenn McGrath as the equal of any he's seen.
Harris' trapped Alastair Cook with the second ball of the day and should have been on a hat-trick when Ian Bell was dropped a ball later by Shane Watson at slip.
Johnson (34 wickets for the series) then cranked up the heat on nightwatchman James Anderson, before Harris returned to remove Kevin Pietersen and Siddle sent Bell packing.
The enthralling exhibition of fast bowling lasted an hour, all before many SCG patrons had found their seats.
At one stage England looked like they'd struggle to eclipse their lowest Ashes total of 45, but even so it was the fifth time this series they've failed to put 200 on the board in an innings.
Rogers half century was the 100th of his first-class career and followed the 36-year-old's match-winning ton in Melbourne.
AUSTRALIA FIRST INNINGS 326
ENGLAND FIRST INNINGS
A COOK lbw Harris 7 (19)
M CARBERRY c Lyon b Johnson 0 (9)
J ANDERSON c Clarke b Johnson 7 (24)
I BELL c Haddin b Siddle 2 (32)
K PIETERSEN c Watson b Harris 3 (9)
G BALLANCE c Haddin b Lyon 18 (51)
B STOKES b Siddle 47 (101)
J BAIRSTOW c Bailey b Siddle 18 (50)
S BORTHWICK c Smith b Harris 1 (17)
S BROAD not out 30 (22)
B RANKIN b Johnson 13 (22)
Sundries (1lb 5w 3nb) 9
Fall: 6 (Carberry), 8 (Cook), 14 (Anderson), 17 (Pietersen), 23 (Bell), 62 (Ballance), 111 (Bairstow), 112 (Stokes), 125 (Borthwick), 155 (Rankin).
Bowling: R Harris 14-5-36-3, M Johnson 13.5-3-33-3 (1w/5 3nb), P Siddle 13-4-23-3, S Watson 3-1-5-0, N Lyon 15-3-57-1.
Batting time: 267 mins. Overs: 58.5.
AUSTRALIA SECOND INNINGS
C ROGERS not out 73 (89)
D WARNER lbw Anderson 16 (20)
S WATSON c Bairstow b Anderson 9 (9)
M CLARKE c Bairstow b Broad 6 (18)
S SMITH c Cook b Stokes 7 (12)
G BAILEY not out 20 (32)
Sundries (9lb) 9
Four wickets for 140
Fall: 27 (Warner), 47 (Watson), 72 (Clarke), 91 (Smith).
Bowling: J Anderson 10-4-36-2, S Broad 7-1-26-1, B Rankin 6-0-25-0, B Stokes 5-0-36-1, S Borthwick 2-0-8-0.
Batting time: 145 mins. Overs: 30.
Umpires: Aleem Dar (PAK), Marais Erasmus (RSA).