United were very unlucky with the nature & timing of the injury - also thought Ole exacerbated things by going to 4 at the back to be honest. As soon as you went to a back four Chelsea attacked Williams both in and out of possession, and he was frequently isolated with Lindelof further away. Rashford has also been under strict instructions to stay high, but there was limited advantage for United there because Azpilicueta just moved wide to man mark him. This effectively meant Chelsea had 2v1 against Williams with Willian & James and had the whole run of that wing. Matic would move wide on occasion but this left Fred 1v2 in midfield which was also a problem.
I also thought clearly the intention was to play on the break, but no one in the back 7 had anywhere near the ability on the ball or passing range required. This meant Bruno had to drop deep, so James and Rashford were increasingly isolated and were left chasing poorly hit prospective passes. Personally I'd say Pogba is all but a requirement in this system - not sure if he wasn't fully fit or needed a rest or what. Once he was on it was a case of too little too late.