MIDDLESBROUGH, England -- Aitor Karanka insisted that one mistake condemned his Middlesbrough team to defeat against Chelsea after a performance he described as "almost perfect."
Diego Costa's 10th goal of the Premier League season proved the only difference between the two teams at the Riverside Stadium, with the Spain international pouncing on a moment of confusion in the Middlesbrough defence following Eden Hazard's corner to hook the ball past Victor Valdes.
Victor Moses and Pedro Rodriguez both missed presentable chances to make Chelsea's lead more comfortable, but Antonio Conte's men were also forced to endure sustained spells of pressure from Middlesbrough in the second half as Karanka's men were roared on by a raucous home crowd.
"Playing against a team like Chelsea, we knew it was going to be a tough game," Karanka admitted. "Once again, we showed we can compete against the best teams in the league and once again one mistake cost us.
"You can't be pleased when you lose a game, particularly at home, but I'm really pleased with the attitude of the players because once again they played the way we have performed in the last month, month and a half.
"To concede a goal from a set piece is a mistake, but I don't want to blame any player because we win as a team and we lose as a team."
The result lifts Chelsea clear at the top of the Premier League for the first time since May 2015. And after the match Karanka highlighted several of the qualities that have made Conte's men so difficult for opponents to compete with in recent weeks.
"They defend together, they are really dangerous in transition, they have a lot of quality in different ways," Karanka said of Chelsea.
"We knew everything before the game and we were almost perfect, but to not lose against this team you have to do it 100 percent, not one mistake."