It was a case of damage limitation at the halftime interval after City raced to a 4-0 lead in an utterly dominant display.
Pep Guardiola's team controlled 62% of possession by the midway point and was ahead after just eight minutes through Foden.
United had already survived one goal-mouth scramble in the opening moments by way of warning of what was to come.
Haaland struck twice in the space of three minutes later in the half, and then set up Foden for the midfielder's second just before halftime.
A number of empty seats appeared in the away section of the crowd, with many United fans failing to show for the second half.
Those that did stay witnessed United's Antony score a wonderful goal from distance after 56 minutes.
But City was soon dominating again, with Haaland completing his treble and then setting up Foden to do likewise.
Substitute, Anthony Martial, scored twice in the last 10 minutes – the second from the penalty spot – but the humiliation had been complete long before.
Guardiola hailed Haaland's latest performance.
"Of course, the quality we have alongside him helps him to score goals. But what he has done, I didn't teach him once," Guardiola said.
"When the ball is right, and he attacks the box, how he moves behind the central defender away from the action, he has incredible instincts that the ball will arrive there and it comes from his mum and dad. He was born with that."
Ten Hag was heavily critical of his players, accusing them of lacking bravery.
"Lack of belief. I've seen some highlights — it was obvious we are defending not on the front foot. We let them play," Ten Hag said. "In possession we were not brave enough, made tactical mistakes, decisions, mistakes and then you get hammered."
Cristiano Ronaldo was an unused substitute, with Ten Hag saying the Portugal great did not deserve to be put through the humiliation of coming on in such a defeat.
"I wouldn't bring him in because out of respect for Cristiano, for his big career," he said.
