England have surrendered a 171-run first innings lead after being bowled out for 155 at tea.
Ryan Harris (3-36) and Mitchell Johnson (3-33) delivered a devastating opening spell, before Peter Siddle (3-23) added his weight to England's second worst batting collapse of a disastrous series.
England resumed on 1-8 but after 70 action-packed 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 126 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 Glenn McGrath has described as the equal of any he's seen.
Harris trapped a brainless Alastair Cook lbw with the second ball of the day, and should have been on a hat-trick after Ian Bell was given a life by Shane Watson at first slip the very next ball.
Johnson then cranked up the heat on nightwatchman James Anderson, striking him twice on his bowling hand in his first over, before dismissing him with his next.
Harris' perfect line struck gold again when Kevin Pietersen prodded another sitter to slip, only this time Watson held on to make it 4-17.
The enthralling exhibition of fast bowling lasted 45 minutes, all before many SCG patrons had found their seats.
But then it was Siddle's turn to take over.
Siddle had Bell caught behind for two in his second over to ensure Australia ultimately lost nothing from Watson's earlier fumble - and claimed Jonny Bairstow and Stokes who also displayed poor shot selection.
At one stage England looked like they'd struggle to eclipse their lowest Ashes total of 45, but even so it's the fifth time this series they've failed to put 200 on the board in an innings.
Johnson has been man of the match on three occasions this series and now has 34 wickets.
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.
Umpires: Aleem Dar (PAK), Marais Erasmus (RSA).