Pedro scored Chelsea's other goal as Antonio Conte's side maintained its flawless away record in the league, keeping it within three points of United and City at the top of the table.
The main talk in west London over the past few days has been a striker who will not be available to Conte in a Chelsea shirt again this season.
United had been expected to rekindle their interest in the Atletico Madrid forward either in January, or next summer, but now reports in Spain suggest their hopes of finally concluding a deal have been dealt a blow.
They struggled to deal with Chelsea's pressing and counter-attack game, but there were also lapses in concentration, with Fletcher's chest-back and Glen Johnson being caught in possession both resulting in Chelsea goals. "He's come here to add and he is doing a great job". He is working very well.
It was the first hat-trick scored by a Blue since outgoing striker Diego Costa in 2014.
The goal of the game saw another sub Cesc Fabregas chip a precise pass into the box, which Azplicueta chested across goal for his second assist of the match, with Morata bundling in from close range. They also hit seven in a match on three other occasions, beating Sunderland 7-2, Aston Villa 7-1 with four goals from Frank Lampard and Stoke 7-0. I told him on Saturday that he puts away all except mine.
Morata's second was even better as he picked up the ball on the left, drove past two Stoke defenders, and curled the shot into the far corner from a tight angle in the 77th.
Diego Costa concedes he is afraid of what fitness coach Oscar Ortega has in store for him after arriving in Spain to complete his move to Atletico Madrid.
"I am pleased for his performance and the performance of the team". I mean I think they're the best of the rest, most certainly.