Despite losing in last weekend's Manchester Derby, City have wrapped up the League in joint-record time, matching United's 2000/2001 title win.
But, just a week after spoiling City's title party by beating their local rivals 3-2 at the Etihad, the way United abjectly gifted the title to their neighbours will sting.
But, he need not to have anxious as West Brom's lone strike through a Jay Rodriguez's header from a Nemanja Matic's poor clearance in the United's vital area finally handed them their third title in seven years.
Herrera had a penalty appeal waved away after seemingly being tripped by Craig Dawson, while Lukaku's powerful drive from Juan Mata's through ball was kept out by the face of Foster.
However, the United manager also gave a strong defence of his own record, listing some of his achievements with Chelsea, Real Madrid and Porto, after being asked how United could expect to overhaul Pep Guardiola's team next season.
Not for the first time this season at Old Trafford United started sluggishly and could have been a goal down after 12 minutes.More news: Ant McPartlin Has Been Banned From Driving
More news: Recommendation Trends to See: Turtle Beach Corporation (HEAR), Amazon.com, Inc
More news: One dead in Crozet plane crash
City midfielder Kevin De Bruyne, a candidate for Player of the Year, said: "Unbelievable season for us". "Manchester City, we've won you the league", was the cry from the West Brom fans.
West Brom took the lead against the run of play on 73 minutes as Rodriguez headed in past De Gea from a corner which came off Matic.
United dominated possession early on, but despite the efforts of Romelu Lukaku and Alexis Sanchez, precious little real impact was made by the home side.
The official was on hand 10 minutes later to book Pogba after attempting to throw the ball in, only exacerbating the testimonial feel at Old Trafford.
"You can't take it for granted", he told Sky Sports on Sunday. "I am pleased we managed to show everyone that". United's threat disappointingly petered out and allowed West Brom to recover.
"It is the number of points they have won".
City were knocked out of the Champions League on Tuesday after their quarter-final defeat by Liverpool, and were beaten by League one side Wigan in the fifth round of the FA Cup in February.