Erik ten Hag has said Manchester United's heavy derby defeat to Manchester City was one of his worst days as manager at Old Trafford.
City cruised to a 3-0 win on Sunday thanks to two goals from Erling Haaland, including a first-half penalty, and another from Phil Foden.
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Ten Hag has suffered some dismal results as United manager, but asked whether the latest defeat to Pep Guardiola's side made it one of his worst days in the job, he said: "Yes."
He added: "Of course, it is disappointing, but last year we had many highlights. When you lose a derby in the way we lose, that is disappointing.
"First half we had a very good game plan and the execution was also very good. It was toe-to-toe first and it was very similar, but then the penalty changed the moment. Then, in the second half we chose to become more offensive and it is 2-0 too quickly. From that point on it was a difficult game."
United have now lost five of their first 10 league games for the first time since 1986 and sit eighth in the Premier League table, already 11 points behind leaders Tottenham.
It is now seven defeats from 14 games in all competitions this season but Ten Hag said he is confident his team are making progress.
"The three games before we won and the spirit is very good," Ten Hag said. "I think we are on the way up. The start was difficult but now we are on the way up. When injuries are getting back we will be getting stronger. We have to be patient but I am happy with some injuries coming back and then our side will be stronger."
Afterwards, Ten Hag said he stood by his decision to drop Raphaël Varane and Sergio Reguilón to the bench in favour of Jonny Evans and Victor Lindelöf while also defending his decision to replace striker Rasmus Højlund midway through the second half after the substitution was greeted with loud boos from the United fans inside Old Trafford.
"I have to protect Rasmus Højlund and I have to protect the team," Ten Hag added.
"He is putting so much effort in pressing, going in the transitions, going the long ways, fighting a tough opposition.
"He is not used to it, three games in a week, so I have to protect him and the team, to bring some energy in. We have bench players, Mason Mount and [Alejandro] Garnacho, we know he can change games."