I still favor Real Madrid to win the match in the second Leg. Although the match will be in Atletico home, Real Madrid seems to have no problem with this. Moreover Real Madrid looks like to have a smaller chance to win La Liga trophy, they will struggle harder in UCL. I'm sure Ancelotti will apply a safer tactic to face Atletico Madrid at their home. Ancelotti and Real Madrid are also have good luck in UCL. So, it is unlikely that Real Madrid to get a lose in the next Leg.
Real Madrid managed to win the match in the first leg so playing in the second leg will be much easier even though the match will take place at Atletico Madrid's home and a crucial match like this is not always profitable even though playing at home because sometimes the result can change and not always the home game will benefit the host. A draw may be much bigger to happen, but it is rather difficult to happen and I predict both teams will play much more carefully.
For Atletico Madrid their struggle will not be easy because if they are unable to score goals faster then the match will be quite tough and it will be much more difficult to get a win if no goals are scored in the first half. It will be a tough match and both teams will definitely do their best to qualify for the next round.