Arsenal have been held to a 1-1 draw by Atletico Madrid in the first leg of their Europa League semi-final, despite playing against 10 men for the majority of Thursday's match at the Emirates Stadium.
Atletico defender Sime Vrsaljko was dismissed for two yellow cards after just 10 minutes, but despite Alexandre Lacazette giving Arsenal the lead, a late goal from Antoine Griezmann has swung the tie in the La Liga side's favour.
Arsene Wenger's team must now score in the Wanda Metropolitano next week to maintain any hope of the long-serving boss experiencing a fairytale finale in Lyon.
Arsenal almost scored a dream goal within seven minutes of kickoff in North London with Danny Welbeck's inch-perfect cross finding Lacazette by the penalty spot, but the Frenchman scuffed his volley wide of the far post.
Arsenal were well on top and the Premier League side were soon gifted a man advantage when Vrsaljko was sent off for two bookable offences, the second of which came as a result of the right-back's studs making connection with Lacazette's ankle.
Diego Simeone was furious with the decision and after taking his protests regarding the lack of a yellow card for an Arsenal player too far, the Argentine was promptly dismissed to the stands.
Arsenal surged forward in numbers as they looked for the goal that their early play deserved, but after Jack Wilshere failed to make the most of a header at the back post, Welbeck fired too close to Oblak after being played in by the midfielder.
Monreal also watched on as a right-footed volley went agonisingly wide of the far post and Atletico remaining on level terms eventually resulted in the Spaniards showing more ambition in the final third.
Their best two chances fell to Griezmann but on both occasions, the French attacker was superbly denied by David Ospina who remained alert to keep out efforts down to his left.
After the restart, the onus was on Arsenal to regain the momentum but although the Gunners were dominating possession, Atletico had set their stall out at the back and were preventing their hosts from creating any clear-cut chances.
However, shortly after the hour mark, Arsenal finally found the breakthrough. Monreal won the ball back just outside of the area and after Wilshere advanced into the penalty area and floated a cross towards Lacazette, the striker did the rest with a header into the corner from eight yards out.
As the match entered the final quarter, Lacazette glanced a header wide of the far post and Granit Xhaka blazed well over the crossbar from distance, but it appeared that Arsenal were going to do enough to take a slender lead to Madrid next week.
That was until eight minutes to go, when Atletico found a potentially-decisive equaliser. Griezmann latched on to a ball over the top and although his initial shot after capitalising on poor defending from Laurent Koscielny was saved, the ball ricocheted back into his path and a second effort from close range found the roof of the net via Shkodran Mustafi.
Arsenal attempted to rally late on with Aaron Ramsey seeing a header superbly clawed away from goal by Oblak, but the English outfit could not force a winner and must find a goal in Spain next week to maintain any hope of reaching the final.
ARSENAL (4-3-3): Ospina; Bellerin, Mustafi, Koscielny, Monreal; Xhaka, Ramsey, Wilshere; Ozil, Welbeck, Lacazette
ATLETICO MADRID (4-4-2): Oblak; Vrsaljko, Gimenez, Godin, Lucas; Correa (Savic 75'), Thomas, Saul, Koke; Gameiro (Gabi 65'), Griezmann (Torres 85')