Well, that's Real Madrid, which we already know as a team that can always show its best performance at the right time. Even at the beginning of the UCL, Real Madrid experienced many difficulties and almost failed to make it to the play-off round, but in the end Real Madrid was able to recover and managed to enter the play-off round.
Real Madrid with their successful history in Champions League, has very strong mentality and confidence in matches there. They have very quality, world class players, good coaches but the main difference between Real Madrid and other clubs in Champions League is tradition and mentality. It affects their approaches and ability to bounce back after getting lead by opponents. Some rich clubs like PSG had many star players, performed well, created big advantage but later lost all very easily. It's because they don't have enough confidence and strong mentality like Real Madrid.
Real Madrid have one foot in the last 16 after winning at Man City's headquarters, but they also need to be careful in the second leg because Man City are very ambitious to turn things around at the Santiago Bernabeu. Man City have enough ammunition to make a comeback in the second leg, but they will have to work to score at least 2 goals to qualify, but Real Madrid will certainly not waste the chance they almost got.
One foot is good but it's not enough and if Real Madrid can make a come back, Manchester City can do it in a second leg too. Real Madrid have good advantage before the second leg match, but they can not underestimate danger and ambition of Manchester City which is undoubtfully a very quality and strong opponent. If Real Madrid play carelessly, Manchester City will certainly are good enough to get a surprising win in Bernabeu.