The bookmakers see Chelsea as the favorite to win against Fluminense; that is why Fluminense was given higher odds than Chelsea, but sometimes odds don't determine the outcome of a game. If Chelsea can struggle to beat Palmeiras in the quarterfinal, I believe there is a chance for Fluminense against Chelsea tonight. Any gambler who feels that Fluminense has what it takes to beat Chelsea tonight can place his money where his mouth is.
I just checked the live betting on Stake and almost all bets chose Chelsea as the winner. I can't imagine if the mafia was against all the gamblers it means that a surprise might happen in this match

honestly I am not confident in choosing one of them to win because somehow my gut feeling says the match might end in a draw so if the match continues through a penalty then the mafia has won the bet. Don't forget the transfer window is still open it means every team needs fresh money, I am not accusing but just anticipating.
I'm more interested in waiting for the big match between PSG and Real Madrid, even though anything is possible but I think both teams will risk their prestige at the same time to prove which team is greater.