Manchester City boss Roberto Mancini believes his free-scoring side need to be even more ruthless in front of goal - like Manchester United.

City have struck 15 times in winning their opening four Premier League games but neighbours and arch-rivals United, who also have a 100% record and top the table, have still scored three more.

When City underlined their title credentials with a 5-1 win at Tottenham last month, United bettered them by thrashing Arsenal 8-2.

Mancini's men impressed again by beating Wigan 3-0 last week, only for United to hammer Bolton 5-0.

Mancini said: "Man United are a top team, they have been used to winning for a long time. They have strong players.

"When they played against Arsenal, when they scored two or three goals, they continued trying to score.

"We need to have this mentality. If we have a game like Tottenham where we can score, we need to continue to try to play."

Mancini, however, does accept that his attack, even with expensive talents such as Edin Dzeko, Sergio Aguero, Carlos Tevez and Mario Balotelli to call upon, will not fire every time.

One such occasion was Wednesday, when City were held to a 1-1 draw by Napoli on their Champions League debut at the Etihad Stadium.

The Italian said: "I think they have played very well, the strikers, but I said it is impossible to score every game.

"Napoli defended very well and it was difficult, but I am happy with our strikers."

The coming months will be a big test of the durability of Mancini's star-studded squad with demanding games both at home and in Europe.

City return to domestic action as they travel to Fulham on Sunday.

Mancini said: "It is important when you play like us - like all the teams playing Premier League and Champions League - you have time to recover between one game and another.

"It is important to recover very well. It is hard but this is football in 2011.

"I don't think it will be possible to win always but we want to try to win.

"We know against Fulham it will be a very tough game because at home they are strong."

City are expected to challenge in all competitions this season and their Champions League opener has been viewed as a disappointing result by some observers.

Mancini, however, was pleased with his side's debut outing in the competition even though they needed to come from behind to claim a point in the Group A clash.

He said: "This can happen in the Champions League, it is a top competition.

"We have players who have played this competition in the past but were playing for the first time with Manchester City.

"We wanted to win but sometimes you lose some balance. We lost this for 10 minutes in the second half.

"I think we made some mistakes but this was normal.

"We had 70 per cent of the possession and I think we missed only a goal in the first half. I am happy after the first game."

The game was a new experience and a learning curve for City but Mancini expects improvement in the next game at German giants Bayern Munich.

He said: "Every game will be hard. Bayern Munich are a top club, they have won everything, but I think it will be good for us."

Mancini is likely to make changes for the weekend trip to Craven Cottage.

Last season's top scorer and talisman Carlos Tevez, who was back on the bench in midweek after starting his first game of the season at Wigan, will hope for a recall.

Tevez, who failed to secure the summer move he craved, now seems to have fallen down the pecking order and Mancini says he must accept that situation.

He said: "I think he is okay.

"In this moment there are players that are better than him but Carlos is here training.

"Carlos will have a chance to play. I don't know if he is happy but every player that can't play is not happy, this is normal.

"In this moment it is like this but he will have his moment."