London, August 17: Steve Smith suffered a major Ashes injury scare when he was struck on the neck by a 92.4mph short ball from Jofra Archer in a dramatic afternoon session at Lord's.
Australia's star batsman retired hurt on the advice of team medical staff before returning to action at the fall of the next wicket, as he chased a third successive century.
But Smith did not last long, advancing from 80 to 92 before being pinned lbw by Chris Woakes.
Australia were soon all out for 250, meaning England led by eight runs.
Smith was attempting to become just the fourth man to make three successive hundreds in one Ashes series, and the first since Arthur Morris for Australia in 1947.
He was back at the crease barely 45 minutes after taking the heavy blow, just below his left ear, that knocked him off his feet.
Archer's delivery had missed the protection provided by Smith's helmet and grille and left the 30-year-old in clear discomfort, although it was unclear whether he was disorientated once he got to his feet.
Despite having been applauded off the field, he faced boos from some spectators on his return to action, an apparently ignorant response to what had been a deeply worrying moment for both teams.
Cricket Australia explained Smith had been cleared to resume his innings, in a statement reported by Cricinfo that read: "Steve was hit on the neck below the left ear. 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 and will now be monitored on an ongoing basis, as is routine."
Just minutes before his bouncer struck the Australia talisman, Archer had bowled a 96.1mph delivery at Smith, which he fended off. Smith was also struck by Archer in a previous over when the batsman was rapped on his left arm as he ducked for another bouncer from the Test debutant.
Smith made two centuries in Australia's emphatic victory in the first Test at Edgbaston but was out just before he reached three figures this time when Woakes broke through his defences. He sought a review, but his body language showed Smith was expecting to walk.
Archer had taken the only previous wicket to fall in the session when he had Australia captain Tim Paine caught, bat-pad, at short leg by Jos Buttler for 23.
Woakes had Peter Siddle caught behind by Jonny Bairstow, which led to Smith's return.
Smith hit three boundaries before England finally found a way to dismiss him for a double-figure score, with Nathan Lyon following later, lbw to Jack Leach, and Pat Cummins caught behind off Broad.
Former England skipper Michael Vaughan condemned the booing of Smith, saying on Twitter that his efforts had been worthy of an ovation.