Ruben Amorim suffered the first major setback of his Manchester United reign as Nottingham Forest capitalised on some poor defending and goalkeeping to secure a shock 3-2 Premier League win at Old Trafford.

The head coach warned that a storm was coming at the start of a week that ended in a second defeat and co-owner Sir Jim Ratcliffe talking about the work required to turn around a club that has become “mediocre”.

Wednesday’s 2-0 loss at Arsenal was compounded on Saturday evening by Forest, with Nikola Milenkovic, Morgan Gibbs-White and Chris Wood securing the club’s first win at Old Trafford since 1994.

United boss Amorim will likely be as frustrated with the manner of the goals as the result.

Corners proved their undoing at Arsenal and Milenkovic headed home from one after just 88 seconds on Saturday, with set pieces continuing to prove a problem after Rasmus Hojlund levelled.

After half-time, United were undone by other issues. Andre Onana was embarrassed by a swerving Gibbs-White strike, with the goalkeeper, Lisandro Martinez and Matthijs De Ligt then all failing to deal with a looping Wood header.

Bruno Fernandes pulled one back but there was no leveller as Nuno Espirito Santo’s side saw out a memorable victory just days after losing 3-0 down the road at Manchester City.

It was a first defeat for Amorim at Old Trafford, where there was a heartfelt pre-match tribute to Kath Phipps after United’s longest-serving employee died this week at the age of 85.

“Thank you, Kath – United legend” read a flag held up by players who then stood behind it during a minute’s applause for the much-loved receptionist who joined the club in 1968.

It was a touching moment before a clash that started with the hosts’ set-piece fragility being exposed inside 90 seconds.

Elliot Anderson sent over a corner and Milenkovic all-too easily beat returning Lisandro Martinez to the ball, powering a close-range header past Onana.

United rallied after that early setback, with Diogo Dalot and Fernandes striking wide from distance before Amad Diallo saw a shot blocked and Matz Sels tipped over a Martinez header.

The hosts kept their foot on the gas and levelled in the 18th minute, with Hojlund turning home after Alejandro Garnacho’s attempt from a Manuel Ugarte ball was smothered by the Forest goalkeeper.

But United took a step back after levelling as their recent set-piece wobbles returned.

First Jota Silva sent a header onto the crossbar after a free-kick was nodded on, then the Portuguese saw a shot blocked for a corner that ended with Murillo drilling just wide.

United skipper Fernandes went close with a set-piece of his own as the first half wound down, hitting a 25-yard free-kick that Sels brilliantly got a fingertip on before it rattled the crossbar.

He would soon be involved in a goal, two minutes into the second half, just at the wrong end.

Fernandes gave the ball away to Callum Hudson-Odoi and he eventually played over to Gibbs-White, whose 20-yard strike swerved as Onana was all too easily beaten.

Forest pushed for another as Ola Aina’s driven ball was struck wide at the far post by Wood, who would soon send the away end wild.

The New Zealand frontman met a deep Gibbs-White cross in the 54th minute with a header back across goal that De Ligt, Onana and Martinez all failed to deal with as it looped in.

United fans and Amorim could not believe their eyes as their side struggled, only to pull one back against the run of play in the 61st minute.

Diallo showed good skill and awareness after driving down the right to play back for Fernandes, who swept the ball past Sels from the edge of the box.

It injected new belief into the Old Trafford faithful, who roared with encouragement when Diallo went close soon after.

But Forest saw out that surge and largely blunted the hosts. Dalot saw an effort saved and Diallo was denied by a block, with the former seeing a wild strike met by groans.

Substitute Marcus Rashford saw a volley deflected wide deep in stoppage time, with Martinez sending an acrobatic effort inches over before the final whistle.