After a comfortable first-leg victory over the third-tier side, Real rested a few of their star players and handed a run to the reserves such as Keylor Navas and Mariano Diaz.
The visitors though were out of their shelves early on, but were unable to make the most of a half chance.
Navas was forced to make the early save following an effort from Garcia from close metres.
An incredible chance fell to Real when Vinicius Da Silva picked out Diaz through on goal, but a last-ditch challenge stopped from getting in on goal.
Real went ahead on 33 minutes when Marco Asensio run into the box led him to find the bottom corner despite a host of defenders surrounding him.
Barely inside minutes, it was two as Asensio completed his brace when good work from Vinicius provided him with an easy finish from close metres.
Five minutes to halftime, it was three when Javi Sanchez turned home a long pass from Asensio into the back of a gaping net.
With the aggregate score now 7-0 at this stage, it was virtually done and dusted for Los Blancos heading into the break.
Their dominance continued in the second half, and after five minutes from returning from the tunnel, it was four.
Spanish international Isco found space outside the box to find the top corner in audacious fashion.
Youngster Sergio Valverde came close to adding a fifth and his name on the scoresheet, but his shot from range missed the target by a whisker.
In the closing quarter, the game dried in the amount of chances with the onslaught from the Whites having seemingly hit the winds from the visitors sail.
The fifth duly came and Vinicius was rewarded for his good work throughout the day when he beat a number of challenges to find the net at the second attempt.
Melila found a mere consolation from the penalty spot after Snachez pulled down Qasmi, and he stepped up to convert from the spot.
Real made it six when Isco collected a clever pass to finish comfortably and book their spot in the last 16.