Third-tier Fuenlabrada hosted the reigning La Liga winners at the 4,000-seater Estadio Fernando Torres, packed to the rafters for the biggest game in the club's 42 year history.
Zidane lined up a team of reserves, handing youngsters the chance to prove themselves in the Copa del Rey. The hunger was evident from the start, as the visitors maintained a high line of pressure to smother their opponents, but Fuenlabrada were equal to it and managed to thwart Madrid's creative play.
The home side's intensity was something Zidane's youngsters found hard to deal with, as they were given few spaces to generate danger around Codina's goal. In fact, the hosts had the first sight on goal when a mix-up between Casilla and Achraf almost saw the right-back inadvertently head the ball into his own net.
The Spanish champions had avoided the temptation of a lethargic start which is so common when higher level teams face lower-tier sides, but they were still unable to find a gap in Fuenlabrada's airtight defence. Towards the end of the first half, Madrid piled pressure on the home side. Marcos Llorente fired a thumping volley from the top of the box, forcing Codina to direct the ball onto the crossbar with his fingertips.
Fuenlabrada looked similarly solid after the break but were penalised with the hour mark just passed when Fran Garcia pulled down Achraf inside the box and the referee pointed to the spot. Marco Asensio stepped up to send Codina the wrong way and hand Real a relieving lead.
The visitors looked more comfortable having broken the deadlock and they piled bodies forward in search of a second goal to sentence the tie. Borja Mayoral was eager to get on the scoresheet but was twice denied by superb stretches from Codina.
However, there was nothing the Barcelona-born keeper could do to deny Madrid from the spot a second time. Theo went down in the area and Lucas Vazquez converted the penalty kick. To pile misery on the hosts, Candela picked up his second yellow and was dismissed seven minutes after coming off the bench.
There was still time for a little more drama when Jesus Vallejo was given his marching orders late on, the young Real Madrid defender going into a reckless lunging tackle on Luis Milla. Real Madrid put one foot in the quarter-finals after coming away with a comfortable two-goal lead going into the return fixture at the Bernabeu.