West Ham were pegged back late on to leave their Europa League play-off with Astra Giurgiu in the balance.
The Hammers led just before half-time, with Mark Noble scoring a penalty after Cristian Sapunaru’s handball.
Slaven Bilic’s side were looking comfortable, but 90 seconds after Michail Antonio missed a chance to double the lead, Astra were level.
Denis Alibec held off James Collins before turning and smashing the ball past Darren Randolph at his near post.
The second leg is at the London Stadium next Thursday (19:45 BST).
Will Antonio miss cost Hammers?
After 80 minutes, Bilic would have been confident his side were heading to the Europa League group stages, against the side who knocked them out last season.
West Ham still have the advantage of an away goal, but Astra’s way back into the tie will be doubly painful as the London side should have been 2-0 up.
Teenager Marcus Browne, who came on for his debut in the second half, broke from his own half and unselfishly squared to Antonio, but the winger shot wide at the far post.
Moments later, substitute Alibec, making his first appearance of the season after playing at Euro 2016 for Romania, smashed home an equaliser from Filipe Teixeira’s corner.
Bilic to name stronger side next week
West Ham made eight changes from the side that lost 2-1 at Chelsea in Monday’s Premier League opener, with Dimitri Payet left in London to rest for Sunday’s game with Bournemouth.
Bilic said that was by necessity to avoid injury, not choice.
Argentine loan signing Jonathan Calleri made his debut up front but had a quiet game, aside from one early header which was saved, before he was replaced by defender Collins after 62 minutes.
Winger Gokhan Tore, making his first start, was impressive with set-pieces, crossing for Sapunaru’s handball, a Reece Burke header which was well saved and an Antonio header which was cleared off the line.
Burke was one of two teenagers starting at the back, along with Reece Oxford, both of whom looked solid on a slow, dry pitch.
But Astra’s late equaliser means Bilic will have to field a stronger side next week if he wants a European run this season.
“We only wanted to rest two or three players – the rest were out because they couldn’t play,” he told BT Sport.
“We wanted to put out a strong team. Next week will be the strongest team available.”
Manager reaction – ‘It is a good result’
West Ham manager Slaven Bilic: “It is a shame, but it is a good result. A couple of minutes before the goal we had a good counter with Marcus Browne but unfortunately we missed the target. Instead of 2-0, and probably killing the game, they get a corner and score.
“We hope we will win the second leg but this was a mixed side with seniors and youngsters. It is a good result. We played with some young kids and it was a great experience for them.”