Real Madrid coach Jose Mourinho admitted that sooner or later his side would taste their first defeat of the season, but added that whoever wanted to beat his side would have to pay a high price.

Mourinho was speaking in the pages of the Monday edition of sports paper Diario AS after watching his side defeat Atletico Madrid in the Madrid derby.

Early goals from Ricardo Carvalho and Mesut Ozil put Real on the way to a fairly comfortable win and the triumph means Mourinho's men have not lost in their last 18 encounters with their city rivals.

"Atletico is a team with a lot of tradition and they were difficult rivals. They gave us problems," admitted Mourinho, who said he was not disappointed his players had not scored more goals.

"Maybe we are tired and it is normal for that to be the case, but playing Atletico means you have to try and keep the ball and for that reason we lowered the pace of our football, rather than because we were tired," he said.

He praised central defender Carvalho, who opened the scoring in the 13th minute of the game with his second goal since signing from Chelsea over the summer.

"He has that ability to pop up in the opposition penalty area, both he and (Sami) Khedira sometimes play almost unnoticed, but I think they were the best players of the night," he commented.

The win maintains Real Madrid's unbeaten start to the season and they have dropped just 4 points from 30 in the BBVA Primera Liga while managing three wins and a draw in their four Champions League matches.

Mourinho was, nevertheless, realistic that sooner or later a defeat would arrive.

"You never know when the day will come, it has to arrive sooner or later, but when it does happen we are not going to give anything away to our rivals," he assured.