Nicolas Pepe's second-half penalty gave Arsenal hope of reaching the Europa League final despite a semi-final first-leg defeat at Villarreal as both teams finished with 10 men.
With the Gunners 2-0 down and a man down after Dani Ceballos' sending off, Pepe stepped up to slot home a vital away goal after Bukayo Saka was tripped.
The result means Mikel Arteta's side head into next Thursday's second leg with real hope of reaching a second Europa League final in three seasons and with the potential of qualifying for next season's Champions League.
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