Manchester United came out on top in a derby-day battle of the spot-kicks to move to within a single point of the Barclays Premiership title.

Given Jose Mourinho's well-aired opinions on the 'new rules' regarding penalties currently in operation in the top flight, there was irony in the knowledge Cristiano Ronaldo's success from the spot, and Darius Vassell's subsequent failure means Chelsea must now win at Arsenal on Sunday if United's visit to Stamford Bridge next Wednesday is not to become a Red Devils party.

Mourinho could have no complaints about United's award, which produced Ronaldo's 23rd goal of the season.

The winger was clearly caught by Michael Ball, with the only criticism surrounding the whole incident being that the City man was still on the pitch after an outrageous stamp on Ronaldo much earlier in the contest.

But for Mourinho the real knife-twister was that after referee Rob Styles ruled Wes Brown had bundled Ball over 11 minutes from time, Vassell could only drive his penalty straight into Edwin van der Sar's legs.

It only maintained an unhappy scoring sequence for City which condemns them to start next season knowing their last league goal on home soil came on New Year's Day.

Not that United will care a jot about that. The title may not quite be won yet but once the formalities are confirmed, it will forever be remembered in Old Trafford folklore as the season they won the league at City.

It is difficult to assess the precise impact the absence of suspended midfielder Joey Barton had on the Blues, although given the erratic state of mind which prompted the ugly training-ground assault on Ousmane Dabo which now leaves the England man facing possible police action, it is probably just as well he was not let loose in such a high-octane atmosphere.

The game was only two minutes old when Ronaldo went down amid a pile of City players clutching his stomach.

Had Styles seen Ball deliberately drive his studs into the man voted both PFA and Football Writers' Player of the Year, he would have been instantly dismissed.

Instead, Styles missed it, although it did not take long for Ferguson to view the incident again on a TV monitor.

The irate Scot came roaring out of his dug out to voice his protests at a truly disgraceful act, which, given the bad publicity City have already endured this week, the Blues could have well done without.

Ball and Ronaldo exchanged brief and unpleasant words when they tangled again shortly afterwards close to the City area and it was hardly a surprise little was seen of the United winger for half an hour or so afterwards.

Revenge, when it arrived, was very sweet indeed for Ronaldo as he goaded Ball into an ill-advised tackle. A veteran of derby-day clashes in both Liverpool and Glasgow, the full-back was not having a very good day all in all and as he made no contact with the ball and chopped at Ronaldo's legs, the penalty award was automatic.

The home fans did their best to put the United man off, twirling some of the 40,000 blue and white scarves handed out before kick-off. But Ronaldo's resolve remained strong and he calmly sent Andreas Isaksson the wrong way.

Not that it was vintage United by any means.

The visitors enjoyed plenty of possession but the draining effects of their Champions League defeat in Milan on Wednesday were obvious and it was City who actually carved out the clearer chances.

Emile Mpenza and DaMarcus Beasley both drove shots straight at Edwin van der Sar as City pushed forward on the counter.

In the absence of Barton, teenage Academy graduate Michael Johnson showed great maturity to hold his own in the midfield exchanges and Nedum Onuoha was equally effective in quelling the threat of Wayne Rooney.

Given the appalling scoring record of Stuart Pearce's side, the hosts - and Chelsea - must have feared one goal would be enough to earn maximum points.

Paul Scholes blasted a shot straight at Isaksson at the start of the second half as United looked to give themselves a bit of extra breathing space.

Largely though, Ferguson's team contented themselves with extended keep-ball sessions, which were only interrupted briefly by City who, in fairness, were not that far off levelling when Mpenza nodded Sun Jihai's corner wide.

The big chance came near the end when Ball went down trying to force his way past Brown.

Vassell struck his shot powerfully enough, only for Van der Sar's long legs to get in the way.

Teams:

Man City Isaksson, Onuoha, Dunne, Distin, Ball,Hamann (Jihai 46), Vassell, Johnson, Ireland (Dickov 69),Beasley (Sinclair 61), Mpenza.

Subs Not Used: Weaver, Samaras.

Booked: Johnson, Dickov.

Man Utd Van der Sar, Brown, Ferdinand, Vidic, Heinze, Ronaldo,Carrick, Scholes, Giggs, Smith (Fletcher 73),Rooney (O'Shea 87).

Subs Not Used: Kuszczak, Solskjaer, Richardson.

Booked: Van der Sar, Giggs.

Goals: Ronaldo 34 pen.

Att: 47,244

Ref: R Styles (Hampshire).