Only down by one goal from the first leg of their Copa del Rey round of 32 tie against Betis, Racing were still well in this game until Perez put through his own net, doubling the verdiblancos lead on aggregate.
Once Sanabria had scored Betis' second of the night from the spot on 59, there was no way back.
Sergio Leon and Gio Lo Celso added two more before full-time in what was a very impressive performance from Quique Setien's side.