Flawed Rooney has one perfect moment as City come up short

Manchester United 2 Manchester City 1

The old Trafford press box was contemplating the prospect of a restive Javier Hernandez soon unseating Wayne Rooney in the Manchester United starting line-up when said No 10 began shuffling back into position for what he says was his first successfully executed bicycle-kick since he wore the uniform of De La Salle School in Croxteth.

One £26m signing (David Silva) plays like a god and misses the 153rd Manchester derby's most elementary chance. Another £26m signing (Rooney) plays like rather less than a mortal and ends up radiating brilliance. Bloody hell, as a United manager once said of football. Can Saturday tell us anything about the balance of power in Manchester football?

It can. Though the afternoon comfortably deconstructed that simplistic notion of City as the malign, unambitious arrivistes and United as football's free spirits – Silva and Yaya Touré showed the exquisite skills that money can buy; City were creative and marginally the better side – it did reveal that world of difference between two strikeforces.

United's remains full of imperfections, Rooney's overall performance reflective of his generally miserable season while Dimitar Berbatov's track record against strong sides remains so poor that Sir Alex Ferguson started without him, just as he has in 22 of United's 43 games against "the big six" since the Bulgarian was signed. While Ferguson was left acknowledging Rooney and Berbatov's faults – "With the abilities those two have got, they should also be dictating games away from home" – he boasts a striker for every occasion. Berbatov's 19 goals have barrelled away the poor sides at Old Trafford, Hernandez's have bought all three of United's away wins, Michael Owen is lurking hungrily in the wings for the run-in and Rooney... is Rooney.

For City, it is a very different story. Roberto Mancini started without Edin Dzeko on Saturday because the Bosnian is taking the time which new overseas strikers often need to make the pace of Premier League football. Will it be four weeks? Six? Mancini is not sure how long, though it was not preposterous to suggest that City must wait until next season to see the best of him. "No," Mancini responded to that. "We have three months left of the season and we will find the solution for him."

This wait would be more palatable if Mario Balotelli – the striker who Mancini went out on a limb to buy – offered fewer uncertainties. Was the decision to send to him for treatment in the freezing environment of Vermont a sign that he is incapable of the self-discipline required to recuperate from the knee injury which has troubled him all season? Has he actually recovered? How much patience does Mancini still have with him? The manager's comments on the topic on Friday suggested it is wearing thin. "I'm not satisfied because it is four weeks Mario is off," Mancini said. "He has a problem with his knee but I hope in the last three months he can play always."

This was a frustration borne of need. Mancini cannot always depend on Carlos Tevez – still the City player with most goals, shots on and off target, free-kicks won, offsides and fouls conceded – and it was for days like Saturday that Balotelli was hired to help. Instead, for the hour's play before Dzeko joined the subdued Tevez, City looked like a side without a striker.

Mancini's problems may get worse before they get better. Don't bank on Balotelli, whose friends and family have worked tirelessly to help him settle, being hungry for a second season in Manchester. There is little more guarantee that Tevez will want to stay put either – the lingering suspicion being that the polite though firm word City chairman Khaldoon al-Mubarak had with him at Eastlands on 21 December – you're staying whether you like it or not, was the bottom line – may have preserved him until the summer, though no longer. If Balotelli and Tevez both leave, Mancini will have to start again.

The summer offers far greater certainties for Ferguson, who will go back to Aston Villa in pursuit of the £15m Ashley Young, but who will want Rooney and Berbatov to heed his criticism of their away form, with consecutive fixtures at Anfield and Stamford Bridge three weeks away.

Mancini admitted only to a mental deficit between Manchester's two teams. "Some [United] players have this mentality that they think, 'Now I can score a goal and change the game'," he said."I think we need to win one cup, one title, because if we do that then we can change the whole mentality of the team."

He might be right: Saturday offered enough evidence. But he is the Manchester manager with thoughts to keep him awake in the small hours.

Scorers: Manchester United Nani 41, Rooney 78 Manchester City Silva 65.

Subs: Man Utd Berbatov 6 (Anderson, 67), Carrick 6 (Scholes, 79) Unused Lindegaard (gk), Brown, Rafael, Owen, Hernandez. Man City Wright-Phillips 7 (Kolarov, 53), Dzeko 5 (Milner, 60) Unused Given (gk), Boateng, K Toure, Vieira, Jo.

Booked: Man Utd Giggs, Scholes Man City Kompany, Milner.

Man of the match Kompany

Referee A Marriner (West Midlands)

Att 75,322.