Full-time: Manchester United 0-1 West Brom
West Brom fans were rightly jubilant at full-time as their team moves seven points clear of 18th-place Sunderland with three games remaining.
The Black Cats have played a game less, it is important to note, but 40 points should surely be enough to guarantee safety for another season.
Manchester United's run of three straight defeats is in stark contrast to the six Premier League wins they recorded in a row between 28 February and 12 April.
With Liverpool's narrow win over QPR earlier today, the gap between the two North West rivals now stands at just four points.
While United should still hold on to their place in next season's Champions League following a one-year absence, Van Gaal will likely be breathing a sigh of relief that Brendan Rodgers' side have endured their own problems over recent weeks.
That is it from us for now, but we will be back in just a few hours' time to provide similar live coverage for the lucrative 'Fight of the Century' between welterweight champions Floyd Mayweather and Manny Pacquiao at the MGM Grand in Las Vegas.
We hope you can join us for what promises to be a truly unmissable piece of sporting history.
The final whistle sounds and Manchester United, despite having monopolised the ball, have suffered three consecutive top-flight defeats for the first time since 2001.
West Brom were content to concede possession for long spells, but their valiant defensive effort, led by Myhill's inspired late interventions between the posts, proved enough to claim all three points after Brunt's free-kick was turned in via a fortunate deflection off Olsson.
For the Baggies, that is there second win in a row at Old Trafford and the first of Pulis' lengthy managerial career against Manchester United.
Manchester United 0-1 West Brom
All hands on deck for West Brom as Lescott and Yacob block efforts from Rooney and Van Persie respectively. Baird then rises high to clear a dangerous cross.
Having looked unconvincing early on, Myhill is now soaring for West Brom and does brilliantly to divert a rasping Di Maria shot over the bar.
A wonderful low save from Myhill after Van Persie connects beautifully with a left-footed effort from 20 yards. Valencia chips the rebound well beyond the far post but he is ruled offside.
Four minutes of additional time signalled and West Brom have made their final change with Liverpool loanee Andre Wisdom on for Gardner to help the defensive effort.
Hugely disappointing from substitute Di Maria as he gets into a good crossing position before slashing the ball hopelessly over the bar. Not good enough by any stretch of the imagination.
Three minutes plus stoppage time remaining.
Van Gaal desperately searching for an equaliser as Falcao comes on for McNair. Still no way through for Manchester United, though, as Rooney sees a hopeful volley blocked.
A frantic mood descends upon Old Trafford as West Brom step up their level of defending from impressive to positively heroic.
Brown Ideye is on for Berahino and Chris Baird replaces the combative Mulumbu.
West Brom somehow still ahead. In the aftermath of the missed penalty, United botched a host of chances to level including a free header from McNair that drifted wide.
Controversy as the referee points to the spot after Berahino blocks Valencia's cross with his left arm. The linesman initially pointed his flag for a corner, but Taylor is convinced.
West Brom are sure the offence occurred outside the box but the initial decision stands after a brief period of deliberation. Van Persie takes but sees his effort saved by Myhill low to the Welshman's left.
Half-hearted appeals for a penalty as Juan Mata's cross is blocked by the arm of Lescott.
20 minutes remaining for Manchester United to find an answer and stop West Brom from pulling off the most textbook of smash and grab wins.
After being on the backfoot for virtually the whole match so far, West Brom snatch the lead as Brunt's driven free-kick takes a huge deflection off Olsson in the Manchester United wall and flies into De Gea's net.
Di Maria is on for Blind.
Goal: Manchester United 0-1 West Brom (Jonas Olsson)
A free-kick in a very dangerous position for West Brom after McNair is yellow carded for recklessly barging into Fletcher just outside the 18-yard box. Brunt and Gardner standing over the ball.
Manchester United, who have had 80% possession, beginning to build real momentum now as they look to break the deadlock. Fellaini falls in the area after a clumsy challenge from behind courtesy of Gardner, but fails to win a penalty.
Herrera then curls a shot wide after a sustained spell of pressure.
A speculative effort from Gardner goes well over following a poor clearance from Van Persie. Manchester United come forward once more, with Fellaini now occupying an advanced role in the final third. Yacob cuts out a cross.
After that early foray from the visitors, the second half is beginning to settle into a familiar pattern as Daley Blind sees a shot blocked by Fellaini, who was standing in an offside position.
The Belgian drew an angry response from Claudio Yacob moments earlier with a strong challenge not deemed worthy of any punishment by referee Taylor.
A warning shot from Rooney who fires straight at Myhill from distance. Young then takes possession from McAuley in the box, yet is penalised for a foul on the West Brom defender.
The second half starts with a rare statement of intent from West Brom as a corner from Gardner almost reaches Dawson but for a timely intervention from the reliable De Gea.
Manchester United have been utterly dominant, yet Pulis will surely be pleased by his side's defensive resolve in that opening 45 minutes.
Van Persie looked sharp early on but was not quite so involved towards the break, but Young remains a bright spark down the left and Valencia is keen to get involved on the opposite side.
West Brom have had a couple of corners, but their focus is understandably on remaining strong at the back and continuing to frustrate.
Manchester United 0-0 West Brom
Valencia stings the palms of Myhill with a fierce shot from an improbable angle after good work from Rooney and Van Persie.
A touch greedy, perhaps, but the Baggies 'keeper did not look confident in dealing with Young's earlier effort and has barely been tested since.
McAuley clears another cross behind and Fletcher comfortably deals with the resulting corner as half-time approaches.
Manchester United in total control of this, yet most of their possession is coming just in front of the West Brom backline and they are struggling badly to find a way through.
Van Persie shapes to shoot but Gareth McAuley makes a strong covering challenge.