Chelsea blew the title race wide open as Frank Lampard's penalty saw them come from behind to beat Manchester United 2-1 at Stamford Bridge.Wayne Rooney put United ahead with a wonderful goal after 30 minutes but Chelsea roared back after the break to equalise through David Luiz. The hosts won the match through Lampard's 80th minute spot kick after Chris Smalling was adjudged to have tripped substitute Yuri Zhirkov.The result leaves Chelsea fourth in the Premier League, still 12 points behind United but with a game in hand, and will be greeted with delight by Arsenal who are now only four points adrift of top spot, also with a match in hand.The game got off to a lively start and it was United who took the lead with through a Wayne Rooney master class.The striker was 25 yards out when he received a pass from Nani and turned to beat his marker before firing a low shot into the bottom left-hand corner of the net.Chelsea were visibly rocked but they should have equalised when Lampard's 40th minute free-kick was saved by van der Sar and the rebound fell straight to Branislav Ivanovic.The defender's bundled effort looked certain to cross the line from only two yards but Edwin van der Sar somehow produced a big hand from nowhere to deny him and then reacted again to divert the ball to safety.Chelsea fought back in the second half and equalised after 54 minutes when Essien's cross from the left got a touch off Ivanovic and fell perfectly for David Luiz to volley home emphatically at the far post.Rooney had a goal disallowed for offside and flashed another chance wide soon afterwards before Chelsea took the lead through Lampard's spot-kick.Zhirkov almost made it 3-1 when his long-distance volley struck Namanija Vidic and then the post.For United it was a bitter blow, made worse when Vidic was sent off in injury time for a second bookable offence.