Australia moved to just six wickets away from victory in the second Test, as England ended on 82/4 without Joe Root, who was out to the last ball of the day.
England's chances of a fight back were already small, but the dismissal of their captain rubbed salt in the wounds and has left Ben Stokes in charge of a mountainous rescue job.
Root's day started and ended in distress after he was hit in the groin area during the pre-play warm-ups, but after battling on he was then struck in a similar area by Starc's 85mph delivery during the closing moments of the session.
He'll eventually recover from his injuries and pain, but England's Ashes might not if they slip to 2-0.
Responsibility now lies with Stokes, who managed a stubborn three runs from 40 balls, and while he'll never give up on a lost cause, he'll need major help from the likes of Ollie Pope and Jos Buttler.
With Root requiring a precautionary trip to hospital, Stokes took charge in the afternoon, and despite Australia at that point ahead with 45/1, England rallied with three wickets for just 10 runs.
James Anderson made short work of Michael Neser, Stuart Broad caught out the off-form Marcus Harris and Ollie Robinson had Steve Smith caught with a lifter into the rib-cage.
But it was another day of mixed emotions for Buttler behind the stumps. His two athletic catches saw off Harris and Smith, but only after he had put down the Australia captain first ball for a third drop of the match.
It added to Broad's poor luck, who can consider himself unfortunate to have not removed Smith second ball, with an extremely tight lbw decision going against him. He celebrated on both occasions, only to be denied by Buttler's handiwork and the umpire.
Following England's rally, Marnus Labuschagne and Travis Head settled Australia with an aggressive stand of 89.
In the absence of the dropped Jack Leach, England opted for occasional spin, with four of the last five wickets shared between Root and Dawid Malan.
Australia's declaration left eight overs for England to bat before the tea interval, but it only took two before Jhye Richardson dismissed Haseeb Hameed.
Rory Burns managed 34 runs from 95 before Richardson built the pressure and snagged the edge, while Malan gave way for 20.
Root and Stokes appeared dead set on holding out for day five, until Starc floored England's skipper, who took five minutes out before hesitantly taking guard. With seconds ticking down to stumps, Root was eventually dismissed after racking up 24 from 67.