Manchester United manager Erik ten Hag said his players were "not ready" to start either half during their 2-2 draw with Leeds United.
Leeds scored 55 seconds after kick-off and again three minutes after half-time to go 2-0 up at Old Trafford.
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Second-half goals from Marcus Rashford and substitute Jadon Sancho earned United a point and while Ten Hag was pleased with the fight back, he admitted his team had paid the price for two slow starts.
"Definitely it was true that each half we are not ready," said Ten Hag.
"I start my talk at half-time with 'hey guys we are not ready, make sure you are ready' and then we go out [and concede again] and that is the point. I am disappointed we lost all the battles in the first minutes of each half.
"You can say we won a point because when you are in a derby and come back from 2-0 down it is good. But on the other hand when you start a derby like we did it's unacceptable. You have to be ready to fight and we weren't ready for the battle."
United headed into the game having won their last 13 games at Old Trafford but needed goals from Rashford and Sancho to come away with a draw against Leeds, who had not won a league game for more than three months and sacked manager Jesse Marsch on Monday.
Sancho came off the bench to score his first goal since September in just his second game back following a spell away from the club during the break for the World Cup.
"I am really happy he is in the right direction," said Ten Hag.
"I hope he can keep his momentum going and I am sure it will strengthen him and motivate him even more. He is a brilliant footballer and if he can invest in the right levels he can be outstanding. We now have a team that can play in the opponents' half, he likes that, he can play in tight areas.
"I really enjoy seeing him playing the way he did with so much confidence, the way he did with so much belief."