I know the CB had a mare yesterday but they've only started playing together this season. We've had to watch Smalling and Jones stink up the place for countless years now. I'm willing to give these two more of a chance, they need more time. Plus, Mourinho spent 60m on the pair he should be getting them to function properly.
Also, I think people are harping on the CB and defence too much. Bigger issue is our style of play, Our inability to deal with teams that press high. Our rubbish build-up play from defence to midfield. No one in this team looks like they know what they're doing. No cohesion on the pitch. All we do is pass it from defence to midfield, the ball never gets up the the attacks at all.
If you don't know how to move the ball effectively, you will always get dispossessed and punished. Yes, the defence should be doing better but It doesn't matters who you have in defence, if you don't know how to play football. You will always end up losing the ball in dangerous areas.
You will also get punished if all you do is deep and try to 'contain' the opposition, we don't try to win the ball back. We just get everyone behind the ball and hope we can snuff attacks out, which goes back to my earlier point about how rubbish we are at moving the ball from one end to the pitch to the other. These tactics are counter productive, they are not conducive to winning football matches, creating chances or scoring goals.