With the tie poised at 2-1 from the first leg, the home side quickly began to dominate the game and duly took the lead in the 18th minute from a strike from Ruben Castro.
Betis all but wrapped the game up in the 28th minute when Vit Benes turned the ball into his own net.
Minutes later it was four when Jorge Molina latched onto a through ball from Nacho and duly dispatched an effort past Spit.
The home side were cruising and looked likely to score on every attack. Braian Rodríguez scored a fifth for Pepe Mel's side and in the 81st minute Xavi Torres completed the rout to seal an 8-1 aggregate win.