Middlesbrough boss Karanka gutted by mistake against Chelsea

But the Spaniard was delighted with much of what he saw.

Diego Costa’s first-half strike – stabbing home from close range after Marcos Alonso’s header, from a corner, cannoned off the unwitting Gaston Ramirez’s back – secured a 1-0 win at the Riverside which extended the Blues’ recent run to six league victories, all of them negotiated without conceding a goal.

Boro gave as good as they got for long periods in the game and, with goalkeeper Victor Valdes in inspired form, might have emerged with something to show for their efforts.

Alvaro Negredo was closest for Boro – forcingThibaut Courtois into a vital save after Adama Traore had found him with 12 minutes remaining – as they pushed, in vain, for an equaliser.

Karanka, whose men remain just a point above the drop zone, said: “Playing against teams like Chelsea, we knew that it was going to be a really, really tough game, but once again we showed everybody that we can compete against the best teams in the league and once again, one mistake punished us.

“To concede a goal from a set-piece is a mistake.

“I don’t want to blame any player because I say always we win as a team and we lose as a team, but when you concede a goal from a set-piece for me, it is a mistake.

“You can’t be pleased when you have lost a game, especially at home, but I am really pleased with the attitude of the players because because playing in the way that we have been doing in the last month and a half, we are in the right way.”

Winger Adama Traore repeatedly threatened to make Chelsea pay for not killing off the game, but ultimately failed to capitalise on a series of chances.

Karanka said: “It’s normal that everybody is excited when he has the ball, but he has the ball three or four minutes in one game and the rest of the game is 87 minutes, so we have to be careful.

“He is doing really well, he is improving a lot, but he has much more to improve and much more to learn. Because he’s young, he can (improve) and, going in this way, for sure he can be a big, big player.” Chelsea boss Antonio Conte is refusing to consider his men Premier League title favourites.

Asked if they are now title favourites after leapfrogging Liverpool and Manchester City, Conte said: “I think we are working very well, but if you ask me what is our target now, I repeat it is very difficult to tell you this.

“I want to wait until the end of the first part of the championship.”

Chelsea have now played 590 minutes of top-flight football since their 3-0 defeat at Arsenal on September 24 without conceding.

He said: “I am pleased because in this league, it is very difficult to have this success and to win these six games in a row is fantastic.”

Middlesbrough: Valdes, Barragan, Chambers, Gibson, Da Silva (Downing 71), Traore, de Roon, Clayton (Fischer 73), Forshaw (Leadbitter 89), Ramirez, Negredo. Subs not used: Bernardo, Rhodes, Guzan, Nsue. Booked: Clayton, Chambers.

Chelsea: Courtois, Azpilicueta, Luiz, Cahill, Moses (Ivanovic 90), Kante, Matic, Alonso, Pedro (Chalobah 80), Costa, Hazard (Oscar 90). Subs not used: Begovic, Fabregas, Batshuayi, Terry. Booked: Azpilicueta, Luiz, Kante. Goals: Costa 41.

Att: 32,704. Ref: Jon Moss (W Yorkshire)