Barcelona B are close to a return to the second division after a brilliant 4-1 win away at Racing Santander on Sunday.
Gerard Lopez's side now just have to maintain their advantage when the two sides meet again at the Mini Estadi next weekend to seal their promotion back to Spain's second tier.
Abdon Prats gave the home side the lead after 13 minutes but Barça B had the lead by the break thanks to two goals from Marc Cardona.
Cardona was on the fringes of the first team in December when he was injured, but has returned at the business end of the season to help his team-mates in their promotion push.
The game swung after the break when Prats was sent off and Barça went on to make the hosts pay with 10 men.
A brace from Dani Romera sealed the handsome win and left the young Blaugrana side in a hugely commanding position in this playoff final.