David Moyes' Hammers have caught the eye as this season's surprise package, mounting an unexpected challenge for the top four and impressing with a bold attacking style. However, this was in stark evidence at Old Trafford as the visitors, bereft of in-form Jesse Lingard - on loan from United - set out to frustrate and stifle Ole Gunnar Solskjaer's side.
Marcus Rashford returned from injury and Dean Henderson kept his place in goal with Victor Lindelof restored to the defence as Fred and Luke Shaw also returned having been on the bench against Milan in midweek.
United had needed extra-time to overcome West Ham in the FA Cup meeting between the sides last month, and the game lapsed into a similar pattern here with Moyes' men deploying a mass defence with a back five and three defensive midfield players.
Henderson punched clear after Aaron Cresswell's deflected, looping cross had threatened to cause problems but it took 25 minutes for United to carve out their first clear opening.
Rashford had recovered soon than expected having picked up an ankle injury in the derby, and it was he whom should have done better as he headed wastefully wide when unmarked at the back post having been picked out by Mason Greenwood.
Greenwood was selected as United's main striker in the absence of Anthony Martial and Edinson Cavani and went close himself eight minutes shy of the interval.
A trademark throw-out by Henderson released the impressive Luke Shaw and he in turn found Bruno Fernandes. The Portuguese schemer in turn picked out Greenwood and his effort looked to be creeping in only for Lukasz Fabianski to get down well and turn the ball on to the post.
Rashford headed wide and Scott McTominay flashed a shot narrowly off target as United ended the half firmly in control.
The second half started as the first had ended - with United on top and remaining patient in the face of the Hammers ultra-defensive system.
Eight minutes after the re-start came the breakthrough that we had been looking for. On 53 minutes, a Daniel James cross almost found Rashford but Vladimir Coufal reacted quickest to turn the ball behind. But, from the resultant Fernandes corner, McTominay's header struck the leaping Dawson and the ball flew beyond the helpless Fabianski to break the deadlock and give United a deserved lead.
The West Ham keeper saved from Fernandes to prevent a second but, with the Hammers now chasing the game, Moyes finally broke the visitors out of their self-inflicted slumber.
Said Benrahma and Manuel Lanzini were brought on to inject some urgency and threat to the east London side, and the changes immediately brought about an increase in West Ham's tempo and danger.
Jarrod Bowen glanced a header wide to serve notice of their renewed intent, even though he was flagged offside so even if he had scored the goal would not have counted.
Henderson was never unduly troubled and in fact it was us that came closest to the game's second goal when Greenwood thumped off a post at the culmination of a trademark sweeping counter-attacking move.
West Ham continued to press but there was never any sense of a late Hammer blow (pun intended) as Harry Maguire and Victor Lindelof were in command at the back to get United over the line and secure a very important win, securing a first league double over West Ham since 2013-14 in the process (when we were managed by a certain David Moyes).
In what amounted to a top four six-pointer, Solskjaer's side moved nine points clear of their visitors in fifth place, to return to second position after Leicester had gone there with a 5-0 thrashing of bottom-club Sheffield United earlier in the day.
With nine games left, it will take an unlikely, Devon-Loch style collapse fo United to miss out on the top four as the season builds to a conclusion.
As a footnote, this was the first time in nine years (February 2012 against Liverpool), in which United didn't make a substitution during a Premier League game.
Overall team performance: 6/10
United Faithful Man of the Match: Luke Shaw