"We didn't score when we had our chances and there's nothing more to add about it".
And Reguilon's performance again showed that he deserves to be starting, with his importance to the team illustrated early on when he made a crucial clearance to prevent Sergi Roberto from latching onto a cut-back from Luis Suarez.
Real are now nine points behind their fierce rivals in La Liga but do have a chance to close the gap on Saturday when the pair meet in the league.
Real coach Santiago Solari stressed his side's dominance in the game but cursed their inability to take their numerous chances.
"But we did not take our chances, and they did".
In the last 15 years, Barcelona have achieved a total of 11 wins at Madrid's home. Football is about goals, being ruthless, and taking your chances, and they did that.
The goal settled a fairly comprehensive 4-1 aggregate win for Barca, who will now face either Valencia or Real Betis in the final. "We have the best players in the world also".
"We're coming through this phase of games - which was really tough [away against Lyon, Sevilla and Madrid twice] - really well". Their mediocre season is being attributed to the departure of their talismanic No.7, Cristiano Ronaldo. He also wasn't on the field when Barcelona routed Madrid 5-1 at Camp Nou in their first league match this season.
In contrast, Suarez had barely touched the ball in the first half but came alive in the crucial moments and would have had a hat-trick had Varane not beaten him to Ousmane Dembele's cross to bundle in an own-goal.
The meeting at the Bernabeu marks the first of two meetings between the clubs in four days, as Real Madrid will host Barcelona again on Saturday in a La Liga match.
Following Barca striker Suarez' audacious Panenka penalty in the 73rd minute of the game, Real skipper, Ramos - who is the active player with the most red cards in El Clasico history - reportedly attempted to keep the floodgates from opening further by telling his teammates to not allow Barca to score any more goals.
It remains to be seen whether action will be taken on this, but if true, it is a truly classless act by the Madrid fans and would need to be addressed soon.