Manchester City defender Pablo Zabaleta says his team's 1-0 derby win over United was essential to keep in touch with Premier League leaders Chelsea.
Sergio Aguero's second-half goal was enough for City to close the gap on Chelsea to six points as they won for the first time in four games.
Zabaleta said: "In the last three games we have not performed well enough.
"Today was a huge game to win to get confidence back and because we can't drop any more points on Chelsea."
|Danny Murphy: "Especially with them playing against 10 men, you might not expect that City would drop deeper and deeper when they went 1-0 up rather than continue pushing forward in search of a second goal, but there were reasons they had that mentality."|
|Read more: How Man City mindset gave Man Utd hope|
City made hard work of closing out the game after Manchester United had defender Chris Smalling sent off for a second booking seven minutes before half-time.
But Aguero's 63rd-minute goal at the Etihad Stadium and first clean sheet in five games gave City the perfect preparation for Wednesday night's home Champions League fixture against CSKA Moscow, according to Zabaleta.
The Argentina international told BBC Sport: "When you play in these kind of games it's always difficult but I think we deserved that win.
"We know how much it means for the fans, for everyone at the club and especially for the players.
"That's the game everybody wants to win. We will let our fans enjoy it but we need to keep our feet on the ground and I think we can still improve.
"We have a very strong squad and great players and now we have to think about the Champions League on Wednesday.
"Winning today has got our confidence back."
City manager Manuel Pellegrini praised the focus of his players for ignoring a number of penalty claims to go on and record a fourth successive win over United.
City had three strong penalty appeals rejected by referee Michael Oliver, with Pellegrini convinced Yaya Toure should have been awarded a spot-kick for a challenge by United defender Marcos Rojo just before half time.
Pellegrini said: "It was important to remain clear and not let it disturb your mind, especially the one against Yaya which was a penalty and also a sending off because it was the last man.
"But we came through that and won the game. It's the important thing when you can win in spite of these things."
City must now look to win their first game in the Champions League this season to enhance their chances of qualifying from Group E after drawing 2-2 in Moscow last month.
Pellegrini is also focused on trying to close the gap further on Chelsea in the Premier League.
He added: "We have 28 games more to play, which is a lot of points. Nobody can know what will happen.
"I said last week we were in a similar position to last year. Nobody knows how it will finish but we will continue to try and retain our title."