When Erik ten Hag warned that Manchester United would unleash their madness on FC Porto, this wasn’t what he had in mind.

What Ten Hag wanted was a response to Sunday’s limp defeat to Tottenham. What he got was another of those crazy European nights from United that have become a hallmark of his time at the club.

Think Bayern Munich, FC Copenhagen and Galatasaray (twice) last season. Four high-scoring games in which United displayed a horrible knack of conceding goals in quick succession, losing three of them and drawing one.

Incredibly, it was the 24th time in two-and-half years under Ten Hag that United have let in three goals or more.

As if it couldn’t get any worse, captain Bruno Fernandes was then sent off late on for the second time in a week on his return to his hometown.

Having inexplicably substituted Marcus Rashford at half-time, Ten Hag replaced both his centre-backs in a last throw of the dice and this time it paid off. Harry Maguire rose to meet Christian Eriksen’s corner in the 91st-minute and equalise with a header that at least spared United another defeat.

But there are plenty of questions for Sir Jim Ratcliffe and the new leadership structure he has put in place at United to ponder as Ten Hag heads into a perilous international break.

He talks about processes and his team being in transition, but just how much have United moved on from the madness of last season? Where is the improvement in his players? What is the evidence of another £200million spent in the transfer market?

Summer signings Manuel Ugarte and Joshua Zirkzee were dropped to the bench here. De Ligt had a shocker. The lack of specialist left-back continues to be Ten Hag’s Achilles heel.

He goes to Aston Villa on Sunday desperately needing to show that his team can still be top-four contenders this season. On the evidence of the last week, they are miles away.

Both these clubs have known better days in Europe than the group stage of the Europa League which saw Porto suffer a shock defeat to Bodo Glimt and United draw at home to FC Twente on matchday one.

United were Porto’s first-ever opponents at the Estadio do Dragao in European competition in 2004 when Jose Mourinho famously went on to win the Champions League in the same month that 20-year-old Samu was born.

A landmark 500th game in all competitions here on Thursday night saw United return to this impressive arena for the first time since April 2009 when they were defending European champions and reached the semi-finals with a stunning goal from Cristiano Ronaldo.

It looked like being another good night when they raced into a two-goal lead, helped by some dodgy goalkeeping from Diogo Costa.

Christian Eriksen, preferred to new £50m man Ugarte in the absence of Kobbie Mainoo, fed Rashford in the seventh minute. He wriggled past Stephen Eustaquio and Joao Mario and unleased a right-foot shot which Costa blocked but allowed to creep over the line.

Rashford was clearly in the mood which made Ten Hag’s decision to replace him with Alejandro Garnacho at half-time all the more puzzling. Defensively, he might not be the best, but his first job is to attack and he was United’s biggest threat.

Rashford was involved again in the 20th minute when he combined with Eriksen to play in Rasmus Hojlund, making his first start of the season due to injury.

The angle was tight but he fired first time to the near post where Costa blundered again, a weak right hand not enough to stop the ball going in again despite Nehuen Perez’s best effort to clear off the line.

Everything was going right for Ten Hag, but as is so often the case with United – especially in Europe – it didn’t take long to start going wrong.

With Diogo Dalot again playing out of position at left-back against his old club, Joao Mario’s crosses from the right were a real problem.

When Noussair Mazraoui headed one towards his own goal under pressure from Samu in the 27th minute, Andre Onana managed to keep it out with a flying save but Pepe reached the loose ball faster than Lisandro Martinez to head in.

Porto pulled level seven minutes later after De Ligt failed to clear his lines despite two attempts. Joao Mario sent over another inviting cross and Samu muscled his way in front of De Ligt to head home.

It was a sixth goal in six games for the powerful Spaniard since making his Porto debut las month, and a seventh wasn’t far behind. When Pepe accelerated away from Martinez shortly after half-time and squared the ball to the edge of the six-yard box, Samu once again got the drop on De Ligt to smash it into the roof of the net.

Fernandes had already been booked for a foul on Alan Varela when he raised his boot towards Perez in the 82nd minute. Was there contact? It didn’t matter. German referee Tobias Stieler produced a second yellow and off he went again.

On went Maguire to provide a crazy end to another crazy game. It was enough to save United from defeat on the night. Whether it will be enough to save Ten Hag is another matter.