All matches between Barcelona vs Real Madrid are El clasico matches. Be it in the Copa Del Rey or the League, even all the games if they meet. The difference is just that the match in the League feels difficult to restore Madrid's chances of winning even though it wins because of the already large difference in points. While the best opportunity I think is in the Copa Del Rey. Madrid still has a chance to qualify for the final.
Of course, Real Madrid will try to win at least one tournament, it is not fitting for the royal club to finish the season without significant victories. They will try to beat Barcelona in the cup and the chances will be equal, as in the last match the game was very equal, until the last I could not give anyone an advantage. But Xavi will want to win all the tournaments in Spain to leave Ancelotti with nothing.
In La Liga it is difficult for Real Madrid to catch up to Barcelona, the Copa del Rey is one of their big opportunities to become champions. The Champions League competition is very tight so it's not easy to determine whether they will be able to win again or not this season. Maybe now they will not focus on chasing Barcleona in La Liga, considering that the chances are very small, we will see them perform completely in the Champions League.
Yesterday's result in the Copa del Rey surprised me. I found a comeback from Real Madrid quite possible, but Benzemá's hat trick and a score of 0-4 in Barça's stadium Camp Nou was very hard to predict. They should not have much trouble defeating Osasuna in the final.
La Liga is a different story: it is almost impossible to close the gap between them and Barcelona, so they will (should) focus in the Champions League, where, although difficult, they still have chances to win.
Today we saw many articles about this game and they even make fun of Barcelona for losing this game but still, the fact is Barcelona is the first team in La Liga and Real Madrid is just racing on Copa del Rey while they lose three El Clasico games against Barcelona and even if this game Barcelona had problems in midfield because they didn't have de Jong and Pedri.