LaLiga leader Atleti lost 2-1 to Cultural Leonesa in the round of 32 last season, and slumped out to Segunda B opposition on Thursday (AEDT).

The 10-time Copa winner fell behind to Adrian Jimenez's sensational flick seven minutes into the second-round tie in Catalonia.

Saul Niguez hit the woodwork and Lucas Torreira went close with a free-kick, but Ricard Sanchez's second booking compounded Atleti's issues as minnow Cornella claimed a famous triumph.

Sanchez was fortunate not to concede a penalty for handball in the opening minutes, before Jose Gimenez, making his 200th Atleti appearance, scythed down Raul Prieto.

With Gimenez, who was booked for his troubles, off the pitch receiving treatment, Cornella added insult to injury, with Agus Medina's cross flicked home expertly by Jimenez.

Atleti seemed set to restore parity shortly after the 20-minute mark, yet Angel Correa saw two efforts blocked either side of Saul hitting the crossbar.

Though Atleti was seeing over 60 per cent possession, it would have been 2-0 down heading into the break if not for Miguel San Roman's save from Pablo Fernandez.

Vitolo got in behind Cornella's backline early in the second half, only for an errant offside flag to deny him a chance to equalise.

Torreira's curling free-kick was inches away from levelling proceedings, though Atleti were then fortunate that Eloy Gila flicked over from close range at the other end.

Sanchez's frustrating night was made worse when he was deemed to have kicked out at Cornella goalkeeper Ramon Juan – the full-back seeing red just 11 minutes after receiving his first booking as Atleti's comeback efforts proved futile.