Manager Jose Mourinho says Thibaut Courtois' red card against Swansea City changed the complexity of the game.
The goalkeeper was dismissed by referee Michael Oliver after bringing down Gomis in the second half as the Blues continue to struggle for form.
The 2-2 against the Swans means that they will have to bounce back straight away when they face Manchester City away from home next week.
"In the first half the result was short, I think we played very well," Mourinho told reporters.
"The team was confident and you could see that. From the moment they equalised until the end of the first half we played with lots of confidence, moving the ball very well, so I'm very happy with what we did in the first half.
"With the penalty, red card, one player less, 2-2 obviously it changes everything. If you have one player less but you are happy with the result, you have a certain approach and normally you can hide the fact you have one player less.
"When you have one player less and you want to try to win it's different; you expose yourself more, the attacking players arrive at a moment where they are so tired they cannot keep the lines compact and it's difficult to press. It changes a lot.
"The good thing for me was that it was a very good first half and in the second half we fought to get a result."
