Rasmus Hojlund’s superb brace fired United ahead twice. But Wilfried Zaha and Kerem Akturkoglu equalised soon after both goals before Mauro Icardi provided the winner.
Andre Onana’s latest calamitous error led to Casemiro seeing red for a second yellow card after having to make a goal-saving foul inside the penalty area.
Icardi missed the spot-kick but was gift-wrapped the decisive strike just moments later to hand Galatasaray their first-ever win on English soil.
Boos projected from United’s disgruntled home faithful at full-time, with a sixth defeat in 10 games intensifying the scrutiny on Ten Hag’s job.
But the Dutchman stresses he hasn’t lost the dressing room and claims he still possesses the United hierarchy’s backing to turn the club’s worst-ever start to a season around.
“Last season was brilliant, terrific, more than we could have expected. But also with this project, we knew there would be gaps,” Ten Hag explained after full-time.
“In this moment, we are in a very difficult period, as everyone can see. But we come out together, we are fighting together, stick together, we are behind each other.
“And that is me, the directors, the team, all together. We will fight. This is not us. We know we have to do better, and in the togetherness, we will come out.”
United were the masters of their own downfall and not for the first time this season, and continued a worrying trend of sacrificing leads within minutes after finding the net.
And Ten Hag admitted he understood why fans would boo his side while they make unacceptable errors that weren’t present during his successful maiden campaign as manager.
