The probability of Chelsea winning against Real Madrid in my opinion is much better in the first leg. Chelsea are playing at home and that should be the reason why they will be favorites to win over Real Madrid.
I don't think Real Madrid are far superior to Chelsea this season. Real Madrid's defense is not good, their midfield is not as good as a few seasons ago and they only rely on Benzema as a goalscorer. You will probably know that there will be a tight guard for Benzema in that match if he is really available, and that man-marking strategy will get Real Madrid in trouble.
Vinicius is the second highest scorer in La Liga and Real Madrid have a large pool of players who can score a goal. But in general, Chelsea in the EPL has similar statistics to Real in La Liga - Chelsea has +38 in goals, and Real has + 34. Real has a 69% percentage of games won, and Chelsea has 60% - here Real have a serious advantage, but it is more likely indicates a lower average level of teams compared to the EPL. In general, I think it will be a fight of approximately equal opponents.