Although the hosts initially looked bright, United finished the first half utterly dominant and 2-0 up thanks to Romelu Lukaku and Chris Smalling, whose goals were three minutes and 11 seconds apart.
"I can expect that Sunday some of them will wake up in the morning and the first thing they think is Jose Mourinho, so I can imagine on Sunday I am going to be criticized for not playing Marcus but it's not my fault, he's suspended", Mourinho said.
Chris Smalling quickly doubled the lead for the visitors seven minutes before the break with a smashing half-volley inside the six-yard box after taking Marouane Fellaini's header onto his chest, 0-2.
Having impressed against Burnley last time out and put in great showings for Spain at the Nations Cup during the worldwide break, it's safe to say that De Gea is back to his best and will be looking to prevent Watford from adding to their tally of 9 goals scored so far this season.
During United's summer tour to the United States, Mourinho hinted Pogba needed to show the same discipline at club level as he did with his country.
United were clinging on - just as manager Mourinho warned - and he said: "I am very happy with the points, I am very happy with the spirit".
After consecutive defeats against Brighton & Hove Albion and Tottenham Hotspur, United are looking a little more settled. With Deeney's bruising, punishing style more than capable of pulverising United's vulnerable centre, Fellaini dropped deep to shield the central defenders to the point where he was nearly indistinguishable from them. "But we had the experience also here last season where they don't give up and when the game is open they believe".
Former captain Gary Neville says that, as a fan, he would be happy to see the 25-year-old leave if his focus was not on United, but Mourinho says the World Cup victor has not told him that he wants to go.
The lead could have been doubled nearly immediately with Foster again called into action, this time pushing a Paul Pogba strike over.
United, backed by their vocal travelling fans, who regularly chanted the name of Mourinho, were establishing a foothold in the game and made their pressure count in the 35th minute.
Despite the victory, United will be disappointed they allowed Watford back into a match that appeared won when Smalling's goal went in.
But Javi Gracia's side came right back into the game in the 65th minute when Abdoulaye Doucoure picked out Gray, who smashed home, giving De Gea no chance. First, there's a three-match suspension to serve after getting a red card in United's last Premier League game for aiming a headbutt at an opponent soon after coming on as a substitute.
Video of the embarrassing gaffe has since flooded social media, but the United boss laughed it off during his pre-match press conference for United's trip to Watford in the Premier League.