Every season, in every title race, there are always key moments in the run-in that can eventually be traced back as the telling blows for whoever wins it and whoever is left with nothing but hard-luck stories. One arrived here for Manchester United and, undoubtedly, they got away with it.

They had been leading through Wayne Rooney's 28th goal of the season and were so dominant throughout the second half that the game should really have been sewn up long before Danny Murphy, the Fulham substitute, burst into the penalty area with the ball at his feet.

Michael Carrick, the wrong side of his man, flicked out a boot and Murphy went down. He had caught Murphy's heel and, though not clearcut, it was not far off. The referee, Michael Oliver, waved play on and we were left to wonder what impact this will have in the title race.

Martin Jol, the Fulham manager, insinuated afterwards that Oliver had simply not been brave enough to award an 89th-minute penalty to an away side at Old Trafford. Jol seemed to be citing Oliver's inexperience, at the age of 27, the youngest referee to officiate in the top division when he was promoted to the Premier League list three years ago. All that can be said with certainty is that he made a bad error of judgment, Carrick was fortunate in the extreme and Jol was so incensed at the time that he actually strode a few yards on to the pitch.

It had been a careless performance from United, dominant yet failing to turn their superiority into the hard currency of goals, and this was the moment they could easily have surrendered the chance to go three points clear of Manchester City. With eight games to go, they will enjoy the view from the top of the table, but the night will be remembered largely for Oliver's generosity.

Jol also argued that Carrick should have been shown a red card, although it was debatable when there were covering defenders. He was correct, though, when he said just about everyone inside Old Trafford knew it was a penalty apart from the man with the authority to give it. Jonny Evans, the United defender, admitted later he was one of them. Sir Alex Ferguson conceded that Carrick "had certainly caught Danny Murphy's heel".

Ferguson's version of events was that United could have had a first-half penalty, when Patrice Evra's cross struck Stephen Kelly's arm, and that this might have been playing on Oliver's mind. He also argued of the Murphy incident that "we deserved that [luck] because we completely dominated the game". United had accumulated 19 attempts at goal and, for long spells, Fulham played as though just determined not to succumb to the kind of ordeal they experienced when the sides met at Craven Cottage in December and it finished 5-0 to the visitors.

Once again, however, the champions did not reach their most sumptuous heights, particularly in the first half when, for the most part, Fulham dealt with them comfortably. The home side's tempo in this period was nothing like as quick as might have been anticipated. More than anything, there was a peculiar lack of urgency. The early onslaught that might have been expected never materialised – in fact, Fulham sporadically looked the more dangerous team – but once Rooney had scored three minutes before half-time the visitors seemed to lose their nerve.

Until the goal there had been no sense that they have one of the least distinguished away records in the top division, with only two wins all season. Here, though, their defending was atrocious. First, Brede Hangeland jumped to meet Ashley Young's cross but misjudged the trajectory of the ball. John Arne Riise was behind Hangeland and probably did not expect his captain, usually so dominant in the air, to do anything but clear the danger. The ball flicked off an unsuspecting Riise and Evans, at the far post, turned it into Rooney's path to scoop his shot past Mark Schwarzer.

The disappointing part for Fulham was that it was such a soft goal to concede when they had begun the game so impressively. This was a hard-working, organised team, with Mahamadou Diarra a tireless worker in front of the defence and naturally attacking players such as Moussa Dembélé and Clint Dempsey also dropping back when needed.

United, however, were clearly superior once they had taken the lead. Rooney's partnership with Danny Welbeck is still a work in progress but, on the wings, Antonio Valencia and Ashley Young were a constant menace. Evans was exceptional while, alongside him, Rio Ferdinand helped make it a difficult evening for Pavel Pogrebnyak before the defender's back problems flared up again and he was forced off. That was the point Fulham started to venture forward and, ultimately, it was a referee's decision that made it a satisfying night for United and an infuriating one for City as well as Fulham.