Arsenal’s hopes of winning the Champions League were dealt a blow after Ousmane Dembele fired Paris St Germain to a 1-0 win in the opening leg of their semi-final at the Emirates.

Dembele opened the scoring inside four minutes before Arsenal had a second-half goal disallowed when VAR adjudged Mikel Merino’s header from Declan Rice’s free-kick was offside.

PSG substitute Goncalo Ramos struck the Arsenal crossbar in the closing moments. Mikel Arteta’s players are now tasked with overhauling a deficit in Paris next week to reach their first final in nearly two decades.

Arteta demanded the greatest atmosphere the Emirates has ever produced but the home supporters were stunned into silence with only three minutes and 17 seconds on the clock.

Dembele, axed by Luis Enrique for Arsenal’s comfortable 2-0 league stage win against PSG here in October, was the architect. The France international picked the ball up in the centre of the pitch and was allowed to run unchallenged before spraying the ball out to Khvicha Kvaratskhelia.

Dembele received the return ball on the edge of Arsenal’s penalty area and fired a left-footed shot into the turf and into the net off David Raya’s post.

It was a nightmare start for Arsenal, who then spent the ensuing 20 minutes chasing PSG shadows.

Kvaratskhelia wanted a penalty when Jurrien Timber put his left arm across the PSG winger’s midriff but his appeal was waved away. Kvaratskhelia was at it again moments later when he was afforded a strike at goal which deflected off Timber’s studs and Raya reacted well.

Arsene Wenger, who took Arsenal to the final of this competition 19 years ago, wore a pained expression alongside Prime Minister Sir Keir Starmer in the director’s box. And so, too, did an animated Arteta as he grew increasingly frustrated with his players, who were so composed against Real Madrid in the quarter-final but so sloppy here.

Desire Doue came close to doubling PSG’s advantage on the half-hour mark but Raya was equal to it with a fine one-handed save. Arsenal were on the ropes and missing the suspended Thomas Partey in the heart of their midfield.

But they came alive in the closing moments of the first period with Joao Neves doing well to disposess Merino as the Spaniard was about to pull the trigger.

On the stroke of half-time, Gabriel Martinelli found himself one-on-one with Gianluigi Donnarumma but the PSG goalkeeper retained his side’s lead with an impressive diving save. Martinelli might have done better, but he might also have been offside when he received the ball.

Arsenal were in need of a strong start to the second half, and they thought they were back on level terms just 90 seconds in when Merino headed home Declan Rice’s free-kick. But VAR intervened with Merino half a body’s width offside.

Rice, so brilliant against Real Madrid but quiet on the night here in a deeper role, broke through the lines and played in Trossard.

On the angle, Trossard took aim at the PSG goal only to see Donnarumma react with another fine save to keep the French side ahead. That was as good as it would get for Arteta’s side.

Arsenal were enjoying more of the ball but they looked short of ideas, with PSG content to protect their lead.

And substitute Bradley Barcola almost added a second with 10 minutes to go when his shot fell narrowly wide before Ramos struck Raya’s woodwork.

Arsenal pushed for an equaliser but in truth, it never looked like arriving and they will head to the Parc des Princes in just eight days trailing in the tie.