Betting on an underdog team is something that I think is very exciting, but if we win then we can win bigger because the odds given are also different. On the other hand, there is no guarantee that the favored team can win, so this is a risk within a risk.

Now that it is clear which teams will compete in the semifinals, Fluminense can no longer be considered an underdog team even though initially many doubted Fluminense could play in the round like now.
With the strength that Chelsea has, is it a big risk to bet on Fluminense?
The Fluminense vs Chelsea match is still not many who dare to draw conclusions on the bets to be made.
If PSG vs Real Madrid, this is definitely a big match.
There is always an underdog in every match, and in the coming match between Chelsea and Fluminense, Fluminense is the underdog since they are the less popular team or club who are yet to possibly achieve half the trophies Chelsea have achieved, while Chelsea is well known around the world and have won alot of trophies in the past.
So, even the odds on sportsbooks clearly shows that Fluminense is the underdog in this match, on stake, they have an odd of 5.40 while Chelsea have an odd of 1.69, that's a very clear difference between the two teams and I guess any sports bettor can easily guess who stand a better chance of winning the match today.