Jermaine Beckford's winner gave League One leaders Leeds a famous FA Cup victory over their fierce rivals Manchester United in a thrilling tie at Old Trafford. Forty-two league places separate the two clubs following the Yorkshire club's dramatic fall from grace during the last decade but Simon Grayson's side showed the rate of their recent revival with a memorable triumph. Man Utd had never before lost in the third round of the Cup - or been knocked out of it by a lower-division side - during Sir Alex Ferguson's 23-year reign as manager, but they began 2010 on the wrong end of their biggest upset in this competition since they were dumped out by Bournemouth in 1984. It was a fully-deserved win for Leeds too, who were full of endeavour coming forward before Beckford outpaced the Man Utd defence to score and, just as importantly, defended as if their lives depended on it afterwards. Grayson's men came into the game unbeaten in 15 games and having lost only twice all season but they were still expected to be brushed aside by the Premier League champions, who themselves have found form since their defensive injury crisis abated. True, Ferguson made seven changes to the side that thumped Wigan earlier in the week, but he kept Dimitar Berbatov and Wayne Rooney together up front and Man Utd should have had far too much fire-power for the visitors to handle. Instead, roared on by 9,000 fanatical supporters, Leeds set about by first frustrating the hosts and then taking the game to them. Man Utd had most of the early possession but Leeds were not panicking when they did get the ball, and stunned the home crowd when they took the lead after 19 minutes. Beckford escaped Wes Brown to latch onto Johnny Howson's superb lofted pass and, although his first touch was poor, he recovered to coolly slide the ball past Tomas Kuszczak and into the bottom corner of the net. It was the kind of finish which showed why Beckford is one of the most sought-after strikers outside the top-flight and might mean Newcastle have to spend a little more than they hoped if they are to prise him away from Elland Road in the transfer window. It almost got even better for Leeds two minutes later when the impressive Howson broke forward down the right and sent over an inviting cross that Luciano Becchio headed wide. Only then did Man Utd come forward with intent and they came agonisingly close to levelling when Berbatov released Rooney down the right. The England striker made for goal and clipped his shot over keeper Casper Ankergren but Jason Crowe got back superbly to hack the ball off the line. Rooney and Danny Welbeck both tried their luck with curling shots from the edge of the box that were both just off target and Jonny Evans headed wide after Ankergren flapped at a corner but otherwise the home side were unable to break down Leeds' determined defence. The game continued in the same vein after the break, with Man Utd pressing but struggling to create clear-cut chances and Ankergren proving a reliable last line of defence when the home side did get a sight of goal. He saved brilliantly from Welbeck but otherwise they failed to really threaten an equaliser until the final half-hour. By then, Antonio Valencia and Ryan Giggs were off the bench - soon to be joined by Michael Owen - and at last Man Utd looked dangerous, only to be thwarted by some dreadful finishing. Owen miscued with the goal gaping after Valencia teed him up and Rooney was also wildly off target when the ball fell to him in the box. Leeds were not just defending either, and could have extended their lead before the end when Beckford fired wide after running through and substitute Robert Snodgrass smashed a rasping free-kick against the bar. There was still time for a couple of desperate goal-mouth scrambles as Man Utd poured forward but in the end one goal was enough to send Leeds through to round four - their first victory at Old Trafford since 1981 - and show why Grayson is rated one the most promising young managers in the game. Source: BBC