London - Australia's Steve Smith returned to make 92 after a sickening blow to the neck before England captain Joe Root fell for the first golden duck of his Test career as Pat Cummins took two wickets in two balls on a dramatic fourth day of the second Ashes clash at Lord's.
England were 96-4 in their second innings - a lead of 104 runs - when rain forced an early close on Saturday.
But with more than 98 overs scheduled for the last day, Australia know early wickets on Sunday could leave them with time enough to press for a victory that would put them 2-0 up in a five-match series.
England will now look to Ben Stokes, dropped twice on his way to 16 not out, and Jos Buttler (10 not out), to keep Australia at bay.
Smith's 92 was the centrepiece of Australia's 250 all out in reply to England's first innings 258.
The star batsman had made 80 when he was felled by a bouncer from fast bowler Jofra Archer, making his Test debut, timed at 92.4 mph.
The ball struck him on the side of the neck and head.
Smith, fell face forward onto the ground. He was wearing a helmet without the additional neck protection that was introduced following the death of Phillip Hughes after his former Australia team-mate was hit by a bouncer in a 2014 domestic Sheffield Shield match in Sydney.
Smith, who had marked his comeback Test following a 12-month ball-tampering ban, with innings of 144 and 142 in Australia's 251-run win in the series opener at Edgbaston, received several minutes of on-field treatment involving both teams' medical staff.
He got to his feet but eventually retired hurt, with Smith receiving a generous round of applause as he walked back into the pavilion.
Archer had previously struck Smith, then on 70, on his unprotected forearm with another bouncer in a fiery eight-over spell that cost 31 runs.
And it was that injury, not the blow to the neck, which Australia said prevented Smith from fielding at the start of England's second innings, with a team spokesman adding later that hospital X-rays had revealed no fracture.
Earlier, Smith resumed his innings as soon as he could after a break of 46 minutes when Peter Siddle's exit left Australia 218-7.
From the second and third balls he faced on his return, Smith hit two fours off paceman Chris Woakes.
But on 92, facing his ninth ball, Smith shouldered arms to a Woakes nip-back delivery and was plumb lbw to leave Australia 234-8.
Smith reviewed almost as an after-thought before replays confirmed the end of a 161-ball innings that included 14 fours.
This series has seen the introduction of concussion protocols designed to allow injured batsmen to be replaced by a substitute -- previously restricted to fielding duty alone.
But the Australia spokesman insisted Smith's health had not been put at undue risk by letting him resume his innings.
"He was assessed lying on the pitch at the instructions of team doctor Richard Saw.
"Dr Saw made the precautionary decision to remove Steve from the field of play to have him further assessed under Cricket Australia's head impact protocol.
"Steve then passed his assessments."
Stuart Broad took 4-65 in 27.3 overs and Woakes 3-61 in 19 while Archer finished with figures of 2-59 in 29.
England then suffered an all-too familiar collapse with World Cup winner Jason Roy, caught and bowled by Cummins off a leading edge.
Next ball, 9-1 became 9-2 with Root caught behind by Australia captain and wicketkeeper Tim Paine off a superb Cummins delivery.
Joe Denly survived the hat-trick but was caught and bowled by Peter Siddle, with the paceman also removing Rory Burns.