- Diogo Dalot (24')
- Antony (52')
- Donyell Malen (43', 44')
- Youssoufa Moukoko (71')
Erik ten Hag's team were made to pay for a poor defensive performance as they fell to their third defeat in four games in the U.S.
United led through Diogo Dalot before Dortmund's Donyell Malen scored twice inside a minute at the end of the first half. Antony equalised in the second half but another mistake at the back allowed Youssoufa Moukoko to score the winner.
Ten Hag's team had the feeling of a reserve side with Harry Maguire, Donny van de Beek and Facundo Pellistri all given starts, but he will still be unhappy with the catalogue of errors which led to Dortmund goals.
It was a night when the Dutchman also made a point with his choice of captain, handing the armband to Scott McTominay despite Maguire's inclusion just a week after stripping the England defender of the armband in favour of Bruno Fernandes.
United started well and took the lead midway through the first half when Van de Beek's lay-off was collected by Dalot on the edge of the box and the Portuguese full-back guided a controlled effort into the corner.
The game, however, began to turn in Dortmund's favour after the 30-minute mark. Youngster Omari Forson was involved in a scuffle with Julian Ryerson and Karim Adeyemi and was substituted shortly afterwards.
The 19-year-old was given encouragement by McTominay and Christian Eriksen as he walked off but got a lecture from Ten Hag on the touchline that lasted nearly a minute.
It looked like United might get in at half-time still in front only for some awful defending to gift Dortmund two quick goals before the break.
First, Brandon Williams was turned too easily on the left and the ball was worked into the penalty area for Malen to score from close range.
Then, just 18 seconds after the restart, Victor Lindelof carelessly gave the ball away to former United midfielder Marcel Sabitzer, who passed to Malen to score his second and make it 2-1.
It almost got worse for United early in the second half.
Maguire played Eriksen into trouble and when Dortmund broke quickly, they were only denied a third goal because André Onana, on as a half-time substitute, made a good save from Sébastien Haller. Onana has been at the club for less than two weeks, but still felt confident to race out of his goal to berate Maguire.
Having narrowly avoided going 3-1 down, United pulled it back to 2-2 when Mats Hummels gave the ball away inside his own penalty area and Antony passed a cool finish into the far corner.
Ten Hag brought on his first-choice stars after 60 minutes but rather than giving United the impetus to win the game, Dortmund soon took advantage of another calamity in defence.
- Ismail Elfath