Middlesbrough boss Aitor Karanka warns of over-confidence against Everton

Middlesbrough boss Aitor Karanka has warned over-confidence could be the greatest threat to his side's chances of securing another top-flight scalp in the Capital One Cup quarter-finals on Tuesday night.

Boro head into their Riverside Stadium clash with Everton - live on Sky Sports 1 HD from 7.30pm - in buoyant mood having moved up to second place in the Championship on the back of successive victories over QPR and Huddersfield.

And they also have no doubt they can cut it on the big occasion having followed up last season's FA Cup win at Manchester City by seeing off Manchester United on penalties in the previous round.

But Karanka warned: "That can be our biggest problem - to think that because we beat Manchester City and Manchester United and played well against Liverpool and Arsenal, the game tomorrow will be easy.

"The reason we did well against those teams is that we worked hard for 90 minutes or more. Just because we are close to the top of the table and we beat Man United in the last round and we're playing at home and will be feeling the atmosphere, to be over-confident would be a big mistake."

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Karanka has a full-strength squad to choose from for the game against Roberto Martinez's Toffees, and could hand Uruguayan striker Cristhian Stuani his first start since he recovered from an injury sustained on international duty.

And he knows full well the threat posed by Everton having struck up a good relationship with Martinez, who was the first to send him a letter of congratulations upon his appointment at the Riverside Stadium in 2013.

Karanka revealed: "He (Martinez) is a person I have to thank a lot because he was the first one I was speaking to when I arrived here. He helped me a lot because in the beginning it was difficult for me and he helped me improve and settle in.

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"He sent me a letter to say welcome and congratulations and he said I had arrived at the best place to be a coach and after two years he was completely right."

One significant piece of advice that could come back to haunt Martinez was his suggestion that Karanka treat cup games in England much more seriously than leading clubs often do in Spain.

"At the beginning we were playing Hull in the cup and he said in Spain teams don't put their best teams in the cup because they don't have the same importance as in the league - but here in England it is different," added Karanka.

"So that helped me, because I was thinking of putting other players in."

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