A catastrophic batting collapse by England on day three of the Ashes has swung the fourth Ashes Test in Australia's favour.
After a strong display with bat and ball on Saturday, the hosts require a further 201 runs in the final innings with all 10 wickets in hand.
Nathan Lyon (5-50) took five wickets as Australia bowled England out for 179 in its second innings at the Melbourne Cricket Ground.
Chasing 231 for victory, Chris Rogers scored 18 and David Warner 12 as Australia moved to 30-0 at stumps.
"To have that result in the second innings for Australia is fantastic to turn the game around," Lyon said.
"We didn't expect that, but we knew if we bowled in partnerships and keep on improving as a bowling unit then we knew that we could possibly crack open the game.
"Come tomorrow Australia has to be really patient with our batting and it's going to be a massive challenge."
Australia had started the day at 164-9 in its first innings and added 40 runs for the last wicket, with Brad Haddin continuing his fine form with 63 runs off 68 balls while Lyon hit an unbeaten 18 as the home side was bowled out for 204.
Batting at number seven, Haddin has been by far Australia's most consistent batsman this series, producing innings of 94 and 53 in the first test, 118 in the second and 55 and 5 in the Ashes-clinching third test at Perth.
Cook run milepost
He was eventually caught behind off Jimmy Anderson (4-67), who had his most productive innings in an otherwise largely fruitless series.
England captain Alastair Cook got his team off to a strong start, but Mitchell Johnson again proved to a thorn in the visitors' side as they lost three wickets for one run in the second session.
It got worse after the tea break, as England's tail folded meekly, losing five wickets for six runs to relinquish its advantage and give Australia a second chance to take control of the match.
England first innings 255
Australia first innings 204
England second innings
Alastair Cook lbw b Johnson 51
Michael Carberry lbw b Siddle 12
Joe Root run out (Johnson) 15
Kevin Pietersen c Harris b Lyon 49
Ian Bell c Johnson b Lyon 0
Ben Stokes c Smith b Lyon 19
Jonny Bairstow c Haddin b Johnson 21
Tim Bresnan b Lyon 0
Stuart Broad c Clarke b Lyon 0
Jimmy Anderson not out 1
Monty Panesar lbw Johnson 0
Extras: (5b,6lb) 11
TOTAL: (all out) 179.
Australia second innings
Chris Rogers not out 18
David warner not out 12
TOTAL: (without loss) 30.
Cook top scored with 51 off only 64 balls - passing 8,000 Test runs in the process - before being trapped lbw to Johnson's reverse swing, and the top order then crumbled.
Michael Carberry was out lbw to Peter Siddle after an exceedingly cautious 12, then in the next over Johnson added a run out to his 31 wickets this series, gathering and firing in a direct hit from mid-off to find Joe Root (15) well out of his crease.
Ian Bell was out for a duck two balls later when he popped up a Lyon delivery to Johnson at mid-off, as England spiraled from 65-0 to be 87-4.
Kevin Pietersen and Ben Stokes temporarily steadied England, but Stokes went 19 shortly after tea, scooping a Lyon ball to Steven Smith at mid-off, and that triggered a hasty capitulation.
Johnson tempted Jonny Bairstow to fish well outside off stump and he was caught behind for 21, exposing the tailenders.
Lyon brought up his 100th test wicket three overs later when he bowled Tim Bresnan without scoring and had Stuart Broad caught for a duck by Michael Clarke at slip two balls later.
Pietersen refused to be intimidated by the effective Australia attack, hitting six boundaries in a defiant knock of 49 before becoming Lyon's fifth wicket when he lofted the ball to Ryan Harris at long-off.
Johnson had Monty Panesar lbw for a duck to end the innings.
Tempers frayed in the late afternoon blustery conditions as Johnson and Pietersen were involved in a confrontation.
The Australian spearhead was upset by Pietersen backing away from his stance when Johnson had completed almost all his run-up, and he threw the ball toward the batsmen's end in frustration.