Following an uninspiring first 60 minutes, Madrid were awarded a soft penalty for a pull on right-back Achraf Hakimi, and with usual taker Cristiano Ronaldo among the stars rested, Marco Asensio calmly rolled in the penalty for 1-0.

Lucas Vazquez then assumed the responsibility and converted from the spot after Theo Hernandez went to ground at a corner, with referee Ignacio Iglesias Villanueva also showing a second yellow card to home defender Paco Candela.

The comfortable win puts Madrid in full control of the tie ahead of the second leg at the Bernabeu in late November.

"I'm very happy with the performance, it is a positive result," the Los Blancos coach told the postgame news conference. "We showed seriousness and intensity from the start. It is a 2-0, clean sheet, and by being patient in the second half we found the gaps."

Zidane had rested all his senior stars for the short trip to the Estadio Fernando Torres, fielding a side made up entirely of squad players and youngsters.

"This is an important competition for me," the former galactico said. "It's true those who played had less time before, but they showed intensity and physically lasted out the game. It means they are all ready to show in any minute. We know the difficulty of the calendar and we are ready for that. We have La Liga [Girona] next, and then the Champions League [Tottenham]."

Spain U21 centre-back Jesus Vallejo, making his debut for Madrid's senior side, was shown a straight red card late on for a foul on Fuenlabrada captain Luis Milla.

"[Vallejo] played a very serious game," Zidane said. "These things can happen. It was a red card, but he played a good game."

Speaking to Gol on the final whistle, Asensio said his side had been aware their lower-division opponents would find it hard to maintain their early intensity through the 90 minutes.

"We knew it was not going to be easy," Asensio said. "The first half they were very strong, but we knew they would drop off a bit after the break. We took advantage and got a very good result."

Asensio is now Madrid's top scorer with six goals (and two assists) in just over 700 minutes of action so far in 2017-18.

"I always try and take advantage of the playing time I get, the more the better," the 21 year old said.