Ji-Sung Park's first-half effort earned Manchester United a hard-fought victory over Arsenal that enabled them to take top spot from their title rivals.
The South Korean improvised superbly to head Nani's deflected cross beyond the reach of goalkeeper Wojciech Szczesny.
Wayne Rooney could have doubled the lead but he blazed a penalty over after Gael Clichy had handled.
Arsenal's best efforts fell to Marouane Chamakh, who missed with a header and had a shot blocked by Nemanja Vidic.
Gunners manager Arsene Wenger would have been disappointed by the paucity of chances created, although his United counterpart Sir Alex Ferguson is unlikely to be eulogising about his side's performance.
Up until the opening goal the first half could be best described as high octane but rather rudderless.
Wenger criticises pitch after defeat at Old Trafford
From the whistle, both sides showed their intent in wanting to win the battle in a jam-packed midfield, with tackles flying in from every angle.
It was surprising that referee Howard Webb did not making a booking until late in the first half given the number of mistimed challenges.
The first yellow card was shown to Arsenal striker Chamakh for a foul on Nani.
Frustration may have caused the Moroccan forward to chop down the United winger, having failed to click with his fellow attackers in the final third during most of the half.
He did manage to work Edwin van der Sar with a tame diving header early on but that was the only time the United keeper was tested during the first 45 minutes.
Arsenal and United took no prisoners with their tackling and closing down but they were guilty of some wayward passing on a skiddy Old Trafford pitch.
However, the home side looked more threatening and had tested the Gunners' third-choice keeper Szczesny a couple of times with long-range efforts from Rooney and Nani, which he comfortably held.
He would have be lucky to get a fingertip to United's next effort - a low angled volley from Nani which flew fractionally wide of the Arsenal right-hand upright.
With 0-0 looking the likely scoreline at the interval, up popped Park to ensure United went in on top.
The South Korean scored his fourth goal against Wenger's side when he arched his neck to meet Nani's deflected cross and beat Szczesny with a looping header.
It was unlucky for the 20-year-old Pole, but he enhanced his reputation 10 minutes after the break by producing a superb block after Rooney had slipped in Anderson.
Phelan delighted with three points against Arsenal
Nani, who is increasing his value with every game, had a better chance moments later but fired over from 12 yards after dispossessing a casual Clichy 20 yards out.
Arsenal also wasted a good chance when Samir Nasri's low angled shot was palmed away by Van der Sar only as far as Chamakh who should have made some space before shooting, but instead had his reflex-reaction shot blocked by Vidic.
The visitors should have paid for the miss when United were awarded a penalty after Clichy slipped and was judged to have handled the ball as Nani attempted to nudge it past him.
Up stepped the usually reliable Rooney, who instead of finding the top corner of the net was closer to finding the top corner of the stand with his wild spot-kick.
That was ugly but Rooney came close to making amends with a thing of beauty late on when he executed a delightful chip which the 6ft 5in Szczesny did brilliantly to tip over.
Arsenal's defeat means they have won none of their last 11 games against United and Chelsea - that sort of form is unlikely to win them the title.
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