Real Madrid manager Carlo Ancelotti praised his side's young players for stepping up and making the difference as they earned a last-gasp 3-2 victory over Leganes in the Copa del Rey quarter-finals with a largely second-string team on Wednesday.

Ancelotti rested several key starters ahead of Saturday's LaLiga derby against Atletico Madrid and next-week's Champions League playoff clash at Manchester City.

After Juan Cruz scored twice for Leganes to cancel out early goals by Luka Modric and Endrick, 20-year-old academy striker Gonzalo Garcia came off the bench to head the stoppage-time winner that sent Real through to the semis.

"We have to be very satisfied with what the young players have done tonight and we have to count on them," Ancelotti told a press conference.

"The youth academy adds up, those who work down below do well and the players arrive prepared. Sure, they lack experience, but that's basically all they need.

"When I put a team together, I do it to try to win the game, not to give minutes to the youth academy. But this year they have had the opportunity due to injuries and other factors and they are doing really well."

In addition to 18-year-old Endrick and 19-year-old Arda Guller who started up-front, Ancelotti gave 20-year-old Jacobo Ramon his first senior start alongside fellow academy player Raul Asencio, who is a year older.

But it was substitute Garcia who grabbed the headlines by scoring the winner a few minutes after coming off the bench, his first goal with the senior squad.

"It was a competitive game. At the back we struggled a bit, Jacobo (Ramon) felt the weight of playing his first game with us a bit, he was a little nervous but then he was more clinical as the game progressed," Ancelotti said.

"Gonzalo (Garcia) is on a very good run with Castilla (Real Madrid's reserve team). Endrick has scored and we have a good feeling working for the team.

"We avoided extra time that would have cost more to recover. We've left players out to be ready on Saturday, so we'll be ready (for Atletico)."