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.