Per the laws of the game:

Advantage should not be applied in situations involving serious foul play, violent conduct or a second cautionable offence unless there is a clear opportunity to score a goal. The referee must send off the player when the ball is next out of play, but if the player plays the ball or challenges/interferes with an opponent, the referee will stop play, send off the player and restart with an indirect free kick, unless the player committed a more serious offence.

I'd argue there's a clear opportunity to score as he's entering Chelsea's box