Atletico have had the upper hand over their city rivals this term, beating them 2-1 on aggregate in August to win the Spanish Super Cup and 2-1 at the Bernabeu in La Liga in September.

Real have struggled to cope with Atletico's high-intensity pressing game and Ancelotti said the team will need to match their opponents for aggression if they are to make it to the quarter-finals and set up a likely meeting with Barcelona.

"Obviously I ask the players to be aggressive in all the games because aggression in defence is a very important component," Ancelotti told a news conference on Wednesday.

"Aggression means working hard to get the ball back when you don't have it, aggression means running fast to block an opponent's cross, aggression means marking effectively at set pieces," added the Italian.

"Aggression in football is an important word and also a positive one."

Real have stuttered at the start of 2015 after a Spanish record run of 22 straight victories that began following September's La Liga defeat by Atletico.

As well as the Cup reverse to their neighbours, they also lost 2-1 at Valencia in La Liga this month, prompting suggestions their victorious trip to the Club World Cup in December may have taken a toll on fitness.

"We know it's an important game at an important moment of the season and we are preparing for it with calm as only if we remain calm will we be able to play our best," Ancelotti said.

"I think the important thing is not to rush things and we don't have to be in a hurry to score early."

Barca, the record Cup winners, have a 5-0 lead ahead of their second leg at Elche on Thursday.

Espanyol and Malaga are already through to the last eight and Sevilla, Athletic Bilbao and Villarreal will join them if they can protect first-leg advantages later on Wednesday.

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