Should we be surprised?
Going into this game, West Brom were 12 points from safety, winless in 15 Premier League away games and had scored just 26 goals this season. And, yet, United could not find a way past them or even mark Jay Rodriguez at a set-piece as he headed the visitors into a shock lead.
Every time you think this United side have turned a corner, an unexpected result brings them crashing back down to earth. This one literally cost them the title.
Mourinho sends message to Glazers
Avram Glazer was among those high-profile figures in the Old Trafford directors box and the club's co-chairman will have taken note of the bench Jose Mourinho selected against West Brom.
Again, there was no sign of Luke Shaw, Matteo Darmian, Marouane Fellaini and Daley Blind and the reality is the quartet would not have made a huge difference despite a pitiful United performance.
Blind has not played in the league since September
These players were all signed after Sir Alex Ferguson's retirement and they could all leave United by the time the window closes on August 31 as Mourinho begins to wield the axe.
Tactics send the wrong message
Mourinho became a household name using the 4-3-3 formation all those years ago at Porto, and he remains loyal to the system.
Usually, Mourinho favors 4-2-3-1 when facing relegation-threatened teams at home but he appeared to have been influenced by Paul Pogba's man of the match display in the Manchester derby ahead of the visit of West Brom.
A three-man midfield helped bring the best out of his talisman at the Etihad, but an extra defensive midfielder played into the Baggies' hands as a narrow United struggled to break them down and the visitors gained confidence.
Pogba failed to build on a brilliant display vs City
On a booking after a bizarre handball, a below-par Pogba was hooked before the hour mark and not even the introduction of the energetic Jesse Lingard jolted United into life.
Martial's drought continues
It only took half an hour. Grabbing the fans' attention as he trotted out for his warm-up, the 'Tony Martial scores again' chants rung around Old Trafford for the first time in a few weeks.
Anthony Martial had to wait until the hour mark to get on the field and, tellingly, was played in his natural position on the left, with Alexis Sanchez pushed out to the right.
But we are still waiting for him to deliver in the same side as United's No.7, who also had an evening to forget.
Victor Lindelof finds his role
Ahead of three games in six days, Mourinho handed Eric Bailly a breather and recalled Victor Lindelof for his second consecutive start at Old Trafford.
And, despite a terrible result, it is clear that the Swede's unique skill set will continue to work in his favor after Mourinho resisted the chance to bring in the fit-again Marcos Rojo and Phil Jones.
"Normally, we are going to have more of the ball and, normally, it’s when we need somebody from the back to add extra technical quality in the middle of the back [four]," Mourinho said pre-match.