Old nemesis Costa pounces to deny Wenger a fairytale finish at Arsenal
Atletico Madrid 1 Arsenal 0
Diego Costa ensured Arsene Wenger's 22-year reign as Arsenal manager will end in Huddersfield and not Lyon as the former Chelsea man hit the winner for Atletico Madrid in a closely fought Europa League semi-final.
Wenger announced last month that he will step down at the end of the season, a campaign now set to end in bitter disappointment and with no silverware following a 1-0 defeat at the Wanda Metropolitano.
The Gunners lost captain Laurent Koscielny early on, reportedly with a torn Achilles, and the visitors' night got worse on the stroke of half-time when Costa notched the goal that secured a 2-1 aggregate win for Diego Simeone's side.
Costa was an unused substitute in London as he recovered from injury, but he more than anyone has exposed the weak underbelly of the Arsenal defence which has undermined Wenger's final years at the Emirates.
Arsenal are likely to finish sixth in the Premier League -their lowest under Wenger - and their new manager will inherit a side not in the Champions League.
This competition offered the chance of a final trophy for the 68-year-old, who took charge of his 250th European game, but it will be Europa League football for Wenger's replacement, with the outgoing boss now set to say his goodbye after the final league game of the season at Huddersfield's John Smith's Stadium.
Early nerves showed for the visitors as David Ospina and Shkodran Mustafi bundled into one another.
Costa, so often a thorn in the side of Arsenal during his time at Stamford Bridge, knew just how to rile the defence.
Arsenal's rearguard suffered a blow inside the opening minutes as Koscielny was carried off on a stretcher, clearly in agony.
Wenger's side enjoyed plenty of the ball but could not muster a shot on goal in the first half, Alexandre Lacazette's heavy touch taking him away from goal.
The hosts appeared content to allow Arsenal the lion's share of the ball and looked to hit on the counter-attack, and they were ahead in first-half stoppage time, Griezmann sliding a pass into the run of Costa, who left Hector Bellerin in his wake before converting.
Aaron Ramsey almost found a route through to Jan Oblak's goal but could only fire wide having been fortunate to collect a fluffed Jack Wilshere strike.
Oblak was finally forced into a meaningful save as he tipped Granit Xhaka's low drive behind, with Mustafi heading the resulting corner over the crossbar.
Wenger introduced Henrikh Mkhitaryan for a struggling Wilshere and he soon thrashed a shot inches over the top.
Costa hobbled off with eight minutes remaining to be replaced by another ex-Chelsea ace in Fernando Torres, who drew a smart save out of Ospina.
Arsenal piled forward but Atletico kept their discipline, which has now seen them go 12 home games without conceding, to seal a place in May 16's final where they will meet Marseille.
The French side overcame Red Bull Salzburg in extra-time, Rolando's 116th minute goal sending them through after Salzburg won 2-0 on the night.
ATLETICO WON 2-1 ON AGGREGATE
ATLETICO: Oblak, Partey (Savic 90), Gimenez, Godin, Hernández, Koke, Gabi, Niguez, Machin Perez (Correa 74), Costa (Torres 83), Griezmann.
Subs not used: Filipe Luis, Gameiro, Werner, Olabe.
ARSENAL: Ospina, Bellerín, Mustafi, Koscielny (Chambers 12), Monreal, Ramsey, Xhaka, Wilshere (Mkhitaryan 68), Welbeck, Ozil, Lacazette.
Subs not used: Iwobi, Maitland-Niles, Kolasinac, Cech, Nketiah.
Man of the match: Diego Costa
Match rating: 7/10
Referee: Gianluca Rocchi (Italy)