Having won all of their previous seven away league matches in which they had conceded first, Solskjaer will be frustrated by his side's poor response in this costly draw at the Hawthorns.

The Baggies went ahead almost immediately when Diagne scored his first goal for the club, his hand in Victor Lindelof's face overlooked, but Fernandes superbly levelled at the end of the first half.

The second period was more open and eventful.

Referee Craig Pawson overturned his decision to award a penalty for a Semi Ajayi foul on Maguire after reviewing the footage on the pitchside monitor, but offside would have come into play anyway he had stuck with his decision.

Johnstone denied Mason Greenwood before Darnell Furlong cleared a Scott McTominay effort off the line, while at the other end David De Gea prevented Diagne securing a shock win with a superb double save.

The recent arrival wasted another great chance towards the end of a match that ended with Maguire on his knees after former United goalkeeper Johnstone tipped his stoppage-time header on to a post.

The Baggies found themselves in the unusual position of defending a lead on Sunday, with Conor Gallagher catching United's backline napping and Diagne outmuscling Lindelof to head past De Gea.

The striker had his hand in the United defender's face when winning the ball, but no foul was called against the loanee and the visitors' response was meek.

Edinson Cavani, on his 34th birthday, failed to connect with a cross and Fred saw a low effort stopped before Marcus Rashford's fine cross was put behind with Anthony Martial lurking.

United were furious to see a goal-kick awarded, adding to Solskjaer's audible anger on the touchline.

Diagne nodded a free-kick wide before De Gea tipped over a Robert Snodgrass header as the Baggies posed problems from crosses.

United were playing poorly and an increasingly frustrated Fernandes was furious to see his penalty claims ignored towards the end of the first half.

But the 26-year-old channelled that annoyance by firing home a stunning leveller, meeting a Luke Shaw cross with a fine hooked effort that flew into the top left-hand corner.

United struggled to create clear-cut chances against Sam Allardyce's well-drilled side, who went close at the other end through Matheus Pereira.

But the visitors looked to have a chance to go ahead when Ajayi was adjudged to have brought down Maguire when attempting to meet a free-kick.

West Brom's players remonstrated with referee Pawson, who was advised to review the foul by video assistant referee Jon Moss on the pitchside monitor.

"You can't not give that as a penalty ref," bellowed McTominay, only to see Pawson overturn his decision to award a spot-kick. The decision to check the foul was an odd one in any case given Maguire was offside.

United went agonisingly close to going ahead in the 70th minute, with substitute Greenwood denied by Johnstone before Furlong cleared McTominay's effort off the line.

Play was now swinging from end to end, with Ainsley Maitland-Niles inexplicably overhitting a cross as Diagne waited to turn it into the net.

But the striker only had himself to blame in the 78th minute as he something he somehow failed to score.

Having shaken off Maguire – perhaps illegally – to go through one-on-one with De Gea, the ball looped up after his initial shot was saved and Diagne looked set to nod into an empty net until the goalkeeper got back superbly to claw away.

Diagne had another chance to grab a late winner, but blazed over from Furlong's cross.

United knocked on the door deep into stoppage time but there was no way through as Johnstone superbly denied Maguire at the death.