England 258 and 96 for 4 (Stokes 16*, Buttler 10*) lead Australia 250 (Smith 92, Broad 4-65) by 104 runs
Steve Smith was always destined to be the headline act, but the way he commanded centre stage at Lord's could scarcely have been more dramatic.
Australia's fortunes in this second Test hung on Smith's performance going into day four with his side desperately needing him to stand up again as they resumed at 80 for 4 in pursuit of England's first-innings 258.
By the end of a day in which Jofra Archer unleashed hell in the form of searing pace and destructive force and Smith had barely withstood the barrage, felled by a nasty blow to the neck and struck hard on the forearm, England held a 104-run lead with six wickets in hand.
The hosts could have been much worse off were it not for two dropped catches at the hands - or not, more to the point - of David Warner, and a failure to review two not-out lbw decisions that replays suggested would have delivered the wickets of Rory Burns and Ben Stokes.
Smith was to be monitored overnight for any delayed signs of concussion, having been cleared to resume batting after initially retiring hurt when he was struck behind the left ear by Archer's short ball. Despite the ugliness of the hit, which knocked Smith off his feet and sent a hush over the shocked crowd as players and medical staff rushed to his side, it was the blow to his forearm, suffered six overs earlier that sent him to hospital for precautionary X-rays.
Smith did not take the field for England's second innings and was replaced by substitute Marnus Labuschagne, although he was later cleared of any fracture and returned to the dressing room, where he sat with his arm in ice. Sense would suggest he should perhaps have rested as a result of being hit on the neck anyhow, and Smith's participation in the rest of the match will depend on how he pulls up on Sunday morning.
The sight of any player being struck on the neck - Smith wasn't using stemguards - was sure to evoke memories of Phil Hughes, the Australian batsman who died after being hit in a similar area in 2014. As awful as Smith looked having collapsed immediately after the blow, he calmed the worst fears by quickly removing his helmet and rolling on to his side and then his back.
Those fears were eased further as Smith walked back to the pavilion, apparently reluctantly, retiring hurt on 80 with Australia 203 for 6, and, when he returned to bat again after Peter Siddle's dismissal, it was to relieved and astounded applause from the crowd, which was blighted by some tasteless booing.
Smith added 12 more runs, including consecutive fours plundered off Chris Woakes before Woakes had him out lbw for 92 two overs later. Smith called for a review, but his dismissal was upheld by the DRS.
Before all the drama, Smith's role had looked pivotal as he and Matthew Wade resumed for the day on 13 and nought respectively, not least in light of Smith's twin tons and Wade's century in the first Test. When Wade was out, Australia needed Smith to turn the match as much as they had at Edgbaston.
Smith and Tim Paine, who made their Test debuts together at Lord's in 2010, looked dangerous before Archer hit his straps with a menacing display that dismissed Paine and turned Smith's body into collateral damage. In one over, Archer's slowest delivery was 88mph and his fastest - at 96mph - did the least damage of the three that hit Smith. Batting with an arm guard two overs after the blow to his forearm, the ball smashed into Smith's gloves as he guided it down safely in front of Jos Buttler at short leg.
In England's innings, Pat Cummins did his best to stretch the tension wire tight by claiming two wickets in as many balls in the fifth over. The hosts' lead was just 17 when they fell to 9 for 2 with Jason Roy out for 2 and Joe Root registering a golden duck.
Roy's dismissal, on the first ball of the over, was somewhat bizarre. He got a leading edge to a short-of-a-length Cummins delivery which bobbled down the pitch slightly to the on side as Cummins pivoted from his follow through to collect the return catch. Cummins then found a thick edge as Root pushed forward and was caught behind by Paine.
Warner put down a low chance to his right off the bowling of Siddle to give Joe Denly a second chance. Nathan Lyon then had an appeal for lbw turned down by umpire Aleem Dar when Burns was on 24 and as Paine declined to review and replays suggested the ball was hitting leg stump. Burns added just five more runs before Siddle had him caught behind. That was after Siddle dismissed Denly, caught and bowled.
Again Australia failed to review as Lyon appeared to trap Stokes lbw, with Hawk-Eye confirming their error. That was after Warner had dropped a chance off Stokes, Lyon again the bowler.