We dont have many good CBs . So this insistence on 3 CBs no matter what the situation, is extremely wierd.
It's served us well since Conte arrived and gives us the flexibility to commit players forward when we have the ball.
It didn't work last night because:
A) Tanganga looked a fucking mess.
B) Sanchez needs to be bossed about by a team mate to look even half effective
C) Doherty has no left foot and shouldn't be playing at all, let alone out of position
D) Chelsea were simply more up for it than we were all over the pitch.