The two clubs will face off for the second time in Group C on Wednesday night.
And Courtois says the Chelsea players are aware of how difficult the clash will be.
"The first game was their first in the Champions League," said Courtois. "If you go to Chelsea, the champions, and maybe they were a bit [in awe]. We played a very good game as well, but I remember the first half was difficult for us.
"After that they gave Roma a really tough game here, they drew twice against Atletico, so we know we face a difficult game.
"They have changed a bit their tactics, they defend better, they have good strikers, and they are fast on the counter. I think they will give us the ball and try to make us make a mistake.
"We are the favourites to win. Our objective is to qualify tomorrow, so that means we have to win.
"For us it's important to start very strong, to try to score early to put the pressure on them, and then hopefully we can have a good game and take the three points back to London."