It was Mourinho’s third consecutive loss after they were beaten 2-1 by Manchester City and then went on to lose 1-0 to Feyenoord in the Europa League.
He was left fuming with Shaw after he failed to get close enough to Nordin Amrabat as Juan Zuniga went on to put Watford 2-1 up.
Speaking about his actions, Mourinho claims Shaw should not have been 25 metres behind his man.
“The first Man City goal and this second goal against Watford — you can find an incredible similarity, which is [Aleksandar] Kolarov has the ball in a difficult situation in the corner and my players, instead of going up to press they decide to give space,” he said.
“And here for the second goal, [Nordin] Amrabat receives the ball and our left-back is 25 metres from him instead of five metres. But even at 25 metres, you have to jump and go and press, but no, we wait.
“This is a tactical but also a mental attitude. It’s something that doesn’t become perfect in a couple of weeks.
“I can split these defeats into three factors — one, the referee’s crucial mistakes are not in my control, there is nothing I can do about that.”
While Mourinho is correct in his analysis of Shaw’s performance, he wasn’t solely to blame for Watford’s goals.
Others on the squad failed to track back and the midfield trio allowed Watford to freely roam through United’s side of the pitch.
It was a poor showing all around and Mourinho will want to make sure the loss streak does not continue against Northampton on Wednesday.