Manchester United must show "a better attitude than anyone else" if they are to close the gap on Manchester City, says manager Ole Gunnar Solskjaer.
United, who lost 2-0 to City at Old Trafford on Wednesday, are sixth in the Premier League table, 25 points behind leaders City.
The derby defeat was United's seventh in nine games in all competitions.
"We certainly got a reaction," said Solskjaer, whose side lost 4-0 at Everton on Sunday."
Second-half goals from Bernardo Silva and substitute Leroy Sane took City back to the top of the table, one point ahead of Liverpool with three games remaining.
"The first half was positive and we were pleased at the break," said Solskjaer.
"Unfortunately, we conceded two sloppy goals in the second half that could have been avoided."
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United are three points off the top four, which will secure Champions League football next season, although they face fourth-placed Chelsea at Old Trafford on Sunday.
"We have to work harder," said Solskjaer.
"The first day of pre-season is going to be a big one and we will see who has looked after themselves in the summer.
"We know we must deliver a good performance against Chelsea."
Solskjaer, who said before the match that defending champions City "will kick you", said manager Pep Guardiola had "set the standards" in the division.
"He had a tough first season but he has turned it around. Living so close to them, we feel it more."
'You do not lose this game'
United striker Marcus Rashford said the performance against City was "not like Manchester United".
"It's not right," he said. "The bare minimum is to work hard and give all for the badge, the supporters, the club and yourself.
"It has been a tough road to get to where we are. To get there and not be putting up the same performances as we were in January is disappointing."
United have lost seven of their past nine games in all competitions, after losing only one of their first 17 following Solskjaer's appointment in December.
Rashford said the players "never call each other out" over their mistakes or performances.
"We have to be real with each other. It's a matter of trying to improve each other," said the England striker.
"Forget the league and top four . You don't lose this game, it's that simple as a Manchester United fan."