Real Madrid's forward Karim Benzema (R) celebrates his opener against Espanyol.

Real Madrid repeated the 1-0 win in Espanyol's Cornella-El Prat Stadium from 10 days ago to go a long way to booking their place in the semi-finals of the Spanish Copa del Rey knockout competition on Tuesday night.

Karim Benzema's headed goal midway through the first half was enough to separate the two sides in an entertaining game in which Real Madrid's superior firepower was again the difference against a rival which once again worked hard, but struggled in front of a side which has kept six clean sheets in a row.

Iker Casillas saved Madrid in the closing minutes as he detained a one on one from Espanyol forward Jhon Cordoba. Casillas stood up tall and the young Colombian didn't have the experience to beat him.

Benzema's goal came after 25 minutes when Alvaro Arbeloa's cross from the right was flicked on and he reached quickly to direct the ball past Kiko Casillla in the Espanyol goal.

Casilla got a hand on the ball, but was unable to keep it out of the net and the Espanyol keeper had been fortunate four minutes earlier when Cristiano Ronaldo hit the inside of the Espanyol post and was unlucky to see the ball bounce along the goal-line without ending up in the back of the net.

In their league meeting 10 days ago, Espanyol had never looked like getting back on level terms after falling behind to Madrid, but on this occasion and with coach Javier Aguirre back on the bench after serving a four match ban, they showed more faith in their ability to get back on level terms and take the tie back to the Santiago Bernabeu Stadium next week.

Sergio Garcia went close for Espanyol ahead of Casillas' save from Cordoba, but the fact is that the away win and the clean sheet make Real Madrid clear favorites to make it into the last 4.

Wednesday sees FC Barcelona travel to face Levante, who held them to a 1-1 draw in the BBVA Primera Liga at the weekend, while Real Sociedad entertain third tier Racing Santander, who have knocked Granada and Almeria out of the competition.

The first leg ties end on Thursday as Atletico Madrid entertain Athletic Club Bilbao in what promises to be the most entertaining tie of the round.