PORTO, Portugal -- Erik ten Hag accused his players of "switching off" as Manchester United blew a two-goal lead against FC Porto to draw 3-3 in the Europa League on Thursday.

United needed a stoppage-time equaliser from Harry Maguire, on as a second-half substitute, to salvage a point in Portugal.

Ten Hag's team were 2-0 up after just 20 minutes at Estadio do Dragao, but conceded twice in seven minutes to go in level at half-time.

United conceded again just after the break and had captain Bruno Fernandes sent off for the second game in a row before Maguire's late goal.

"It's mixed feelings," Ten Hag told a news conference.

"We scored two great goals and then we switched off. We don't keep possession and defending, we're switching off. We concede the first goal totally unnecessary and then you light up the fire in this stadium and it becomes very tough.

"We addressed it at half-time and then you concede a third one, so unnecessary. It's no good defending again. That's also to do with some willingness in some moments.

"But then I have to praise the guys, how they return in the game and how they fight and find a way to get an equaliser."

Ten Hag was also forced to defend his decision to substitute Marcus Rashford at half-time.

Rashford scored United's opening goal and looked sharp all night but was surprisingly replaced with Alejandro Garnacho at the break.

Ten Hag initially said Rashford was substituted to keep the forward fresh ahead of the trip to Aston Villa on Sunday.

But speaking in his news conference, the Dutchman hinted he had made the change after both of Porto's first-half goals had come via crosses from Rashford's side of the pitch.

"Garnacho was my best player on Sunday by far and also in many other games," said Ten Hag when asked why Rashford was substituted.

"I think in the season as I assess it so far, he is bringing us so far the offensive threat by creating chances, assists, also scoring. Garnacho, we also had to play him as well and we have two very good players over that side.

"I have to watch [the game] back and I think over the left side definitely we didn't defend well tonight and Marcus also played a part in this. But, as I say, it had to do with Garnacho and nothing against Rashy."