Ten-man West Ham kept their hopes of reaching a first European semi-final since 1976 alive by battling to a draw in the first leg of their Europa League quarter-final with Lyon at London Stadium.
Aaron Cresswell's red card for bringing down visiting skipper Moussa Dembele when he was the last man in first-half stoppage time changed the complexion of a tie that David Moyes' men were starting to grow into.
Despite the setback Jarrod Bowen put the Hammers in front seven minutes after the re-start when he seized on a Jerome Boateng mistake in his own box and finished on the turn.
But it was a rare glimpse of goal for the home side, who were forced to defend for long periods. Their defences were eventually breached by on-loan Tottenham midfielder Tanguy Ndombele, who tapped home from close range after the ball had been deflected into his path.
Alphonse Areola denied Emerson with a decent save as Lyon searched for a winner but West Ham held firm, with Craig Dawson particularly impressive in their rearguard action.
If there is any consolation given how the game unfolded, it is that the Premier League side are still in with a chance, unlike the last occasion West Ham reached a European quarter-final, when they were beaten 4-1 in the first leg at home by Dynamo Tblisi in 1981.
Relive West Ham's Europa League quarter-final first leg against Lyon
"We have a really difficult game in Lyon now but we expected that - it's very much all to play for and I would have taken that the way we ended the first half," said Hammers boss Moyes.
"It was not a good performance but it was a good, resilient performance defensively."
Defender Craig Dawson felt the Hammers showed "great courage" to respond to the setback of Cresswell's red card.
"The gameplan changed and we created a couple of chances and worked really hard, but I wouldn't expect anything else," said Dawson.
"The group here is special - togetherness carries us forward. It comes from the manager. With his experience, he works hard for us and gives us the belief we can do it."
Frustration turns to satisfaction for Moyes
Bowen's goal triggered euphoric scenes in the stands and a fierce reaction from Moyes, who was feeling pretty aggrieved at how the game had been panning out.
Dembele's unnecessary wink as Cresswell made his way off was reminiscent of Cristiano Ronaldo's infamous reaction to Wayne Rooney's dismissal during the 2006 World Cup.
As on that occasion, there was controversy over the decision.
However, Cresswell certainly grabbed former Fulham and Celtic striker Dembele's arm after the Lyon player had run past Kurt Zouma and once referee Felix Zwayer determined the full-back was the last man, the outcome was inevitable.
Moyes waited for Zwayer at the interval to offer his opinion, unhappy about a perceived foul on Bowen in the build-up to the dismissal, to which the German reacted by booking the Hammers manager.
"The tackle on Bowen leading up to it [the red card] was a foul - I would have expected VAR to intervene, it was the same phase of play," insisted Moyes.
"But we are still in with a good shout - we didn't play well and we can only play much better next week," he added to BT Sport.
The West Ham boss had already been unimpressed with the official given he had twice stopped play for an injury to a Lyon player which was not head related.
But the Scot's real frustration was reserved for a fan who ran onto the pitch and forced the game to be stopped just as West Ham were pushing forward on a rare attack close to the Lyon box.
Lyon boss Peter Bosz, meanwhile, was unhappy his side failed to make the most of their numerical advantage in the second half.
"We had to win, we played half a game against 10 men. When you play against 10 players you should be winning but we conceded a silly goal," Bosz said.
Bowen again proves his importance to Hammers
Former Hull man Bowen is clearly going to be a key figure in the return leg.
Bowen had been a doubt for the game with the heel injury he suffered at Liverpool last month that kept him out of the last-16 win over Sevilla.
But, even in a side down to 10 men, he remained a danger and was lurking behind Boateng - but in an onside position - as the German failed to deal with a routine break of possession in the centre of the penalty area.
It was a priceless effort against a Lyon side who are a shadow of the team that beat Manchester City on their way to reaching the Champions League semi-final two seasons ago.
Nevertheless, Moyes spent a good portion of the build-up stressing how important it was for neither his players nor supporters to forget the tie would not be decided for another week, and that they should not get frustrated if the game lacked the fizz of that marvellous victory over Sevilla three weeks ago.
Despite the potential for a semi-final with Barcelona - which some long-time Hammers fans believe would be the biggest match in their history, even taking account of previous trophy successes in the FA Cup and European Cup Winners' Cup - they heeded the advice.
Their momentum was halted by the red card. With 11 men in France, Moyes can be optimistic about picking it up again.