Head to Head in the last five matches Barcelona has excelled and this will be a big capital for them, plus the match will take place at Camp Nou. But if you look at the readiness of the two, Real Madrid also has the opportunity to turn things around and will secure victory while ensuring qualification for the final. I'm sure Ancelotti will surprise this match and hope it will be a tense match.
Barcelona has played well in every match against Madrid since Xavi took over as Barcelona's coach. Barcelona won the first leg of the Copa del Rey even without their leading scorer Lewandowski in their squad. Barcelona's gameplay was steady. The players are very confident now. Barcelona's defense is also strong now. If Barcelona's attacking players Lewa and Rafinha can play well against Madrid then I guess the Barcelona team can win again against Madrid.
Basically, Barcelona certainly has a better chance of still winning in this second leg, or just playing defensively is enough for Barcelona to maintain the aggregate victory it has. But yes, because Real Madrid is a top team which of course has many ways to rise, so Real Madrid will still have the chance to win too even though these results will certainly be difficult to obtain.
Apart from that, if I consider the odds factor given by the bookies, then Real Madrid still looks to be able to play well in this match. Therefore, it is not surprising that Real Madrid will be able to turn things around but for me personally, I still believe that Barcelona is indeed better at this moment.