Ruben Amorim admitted Manchester United "have a lot to do" after they suffered a 1-0 defeat to 10-man Everton on the one-year anniversary of his first match in charge.

Idrissa Gueye was sent off 13 minutes in after getting into a fight with Michael Keane and striking his team-mate in the face.

Everton scored their winner in the 29th minute, with Kiernan Dewsbury-Hall skipping past two tame challenges to bend his strike past Senne Lammens, who got a hand to it.

As such, United lost a Premier League game at Old Trafford after seeing the opposition pick up a red card for the first time ever, winning 36 and drawing 10 of the previous 46.

That is despite the Red Devils having 25 attempts, with 23 of those coming after the sending-off, and six of those on target as they accumulated 1.7 expected goals (xG).

United were greeted by boos from the home crowd at full-time, and Amorim was also disappointed, particularly with the lack of intensity his side showed.

"Really frustrated, like any other person that supports Man Utd," he told Sky Sports.

"The way we started the game, the way we didn't understand how we should play against 10 men. They deserved to win. Even suffering with 10 men, that is normal.

"We had a lot of chances, but the quality and the decision-making was not there. The understanding of every situation of the game was not there. And then the quality near the box.

"But the most important is the intensity. You can feel it right away when we start the game. In the first minute, you can feel when we are at the top level of intensity and when we are not. Then, when we are not, we cannot win in this way.

"Of course [he is surprised]. But I said in many occasions that I understand that we have a lot to do. But I am really frustrated with the way we played the game, especially at home, and understanding what happened this weekend with the other clubs, looking at the table and feeling everything.

"And the way we presented from the first minute is really frustrating."

United have now failed to win any of their last 10 Premier League games when trailing at half-time (D2 L8), since coming from behind to beat Southampton 3-1 at Old Trafford in January.

Amorim's side, who were on a five-game unbeaten run, missed the chance to move up to fifth and take advantage of other teams above them dropping points this weekend, instead staying 10th.

"This is more than [a missed opportunity]," added Amorim. "We need to play the game in a different way.

"Sometimes we can do it, sometimes we can have good runs of results and performance, but sometimes we drop."