Danny Ings scored the first European goal of his career but West Ham’s winning streak on the continent this season was ended by a 1-1 draw away at Belgian side Gent.
Ings tucked away Jarrod Bowen’s cross on the stroke of half-time - thanks in no small part to a Gent ball boy - to give them the lead in the first leg of the Europa Conference League quarter-final.
But West Ham’s defending let them down after the break as they allowed Gent forward Hugo Cuypers to equalise, leaving the tie finely poised heading into next week’s second leg at the London Stadium.
The Hammers may be struggling in the Premier League, but their European exploits - they came into this game with a perfect 10 out of 10 win record - have raised genuine hopes that a miserable season could yet turn into a memorable one with a first trophy in 43 years.
However, it was a ragged first half from the visitors, with Ben Johnson making a timely block to prevent Cuypers from firing home while both Kamil Piatkowski and Joseph Okumu headed over from corners.
West Ham thought they had taken the lead, against the run of play, when Gent goalkeeper Davy Roef dropped Bowen’s corner under pressure from Nayef Aguerd, but a VAR check ruled it out for handball by the Morocco defender.
However, they did edge in front on the stroke of half-time when Vladimir Coufal caught Gent napping with a quickly-taken throw.
Boss David Moyes has fallen foul of ball boys in Europe before; he was sent off for kicking a ball at one in their semi-final defeat at Eintracht Frankfurt last season.
But he was grateful to the Gent youngster who lobbed the ball straight to Coufal so the right-back could immediately find Bowen in the box.
Bowen squared the ball across goal and Ings, on his first European start since October 2015 for Liverpool, tapped in at the far post.
The goal was subject to another VAR check, this time for offside, but the decision went the way of the Hammers to delight the 1,000 visiting fans squashed into the corner at the opposite end.
However, Gent dragged themselves level in the 57th minute when West Ham failed to track their runners.
Angelo Ogbonna was nutmegged and Cuypers sidestepped Johnson too easily before finishing past Hammers keeper Alphonse Areola.
Bowen could have put West Ham back in front after he was sent through by Lucas Paqueta only for his attempted chip over Roef to roll wide, while Gent’s Nigerian striker Gift Orban hit the crossbar with an overhead kick.
There was confusion in stoppage time when home defender Piatkowski was sent off, and then reinstated after a review, for bringing down Paqueta.
Moyes was angry that Gent were given back the ball as his side chased a winner, but moments later the final whistle blew and it is all to play for in seven days’ time.
