Diego Simeone's side were sluggish for much of Friday's (AEDT) encounter at Reino de Leon, though Angel Correa's 62nd-minute strike seemed set to send Atleti through.

However, third-tier side Cultural fought back - Julen Castaneda's venomous volley forcing extra-time.

And it was Benito - who had earlier missed a glorious chance to open the scoring - who had the final say, his precise volley in the 108th minute sparking huge celebrations from the home fans as Cultural claimed the unlikeliest of scalps.

Atleti wasted little time in stamping their authority on proceedings and Vitolo should have done better when he raced through one-on-one with Lucas Giffard only to prod wide in the clearest opportunity of a tepid first half.

Benito should have made Atleti pay for Vitolo's profligacy when he met Virgil Theresin's cross, but the Cultural striker diverted his close-range header over.

Vitolo looked all set to break the deadlock just before the hour, though he yet again fluffed his lines when up against Giffard.

Atleti's luck changed three minutes later - Correa keeping his cool to pick out the bottom-left corner after latching onto Joao Felix's sublime flick.

Cultural's hopes seemed to be dashed, but Castaneda had other ideas, with the left-back's volley hauling the hosts level.

Ivan Saponjic missed two glorious chances to restore Atleti's lead, before Giffard made a sensational double save to force extra-time, setting the stage for Benito.

Gabriel Gudino's lofted pass opened up Atleti's defence and, showing the composure he had sorely lacked with his earlier chance, Benito sent a crisp volley arrowing in at the near post to seal an incredible win.