Atletico Madrid captain Gabi believes that Koke is on the road to becoming a key player for the club and for Spain.
The pair featured in Real Madrid's 1-0 defeat to the Colchoneros, in which Diego Costa's goalscoring streak continued with an early strike which ultimately sealed the three points in the visitors' favour.
"Costa is very important to the way we play," Gabi told reporters.
"For his forward runs, his capacity to sacrifice [individual gains for the team], the delivery he puts on every ball, and how he holds the ball up in front of goal.
"Koke is going to be a fundamental player for Atletico and for the national team. He's world class."
Gabi also insisted that the players were convinced they could conquer Carlo Ancelotti's men following last season's Copa del Rey final win, despite not having beaten them in La Liga since 1999.
"We approached the derby in a different way to how we had done in the past," the midfielder added.
"We knew it was possible to win at the Bernabeu after what we did in the Copa del Rey final, but also that they would be more attentive.
"Atletico played a 10 out of 10 game. This time we knew that a win was possible and that statistics are there to be broken."
Vicente Calderon summer signing David Villa revealed his satisfaction with beating the Blancos - against whom he has battled on numerous occasions with Barcelona and Valencia in the past.
"My first Madrid derby was unforgettable!" he wrote on his official Twitter account. "The whole team were immense."