Juan Mata struck an 87th-minute winner as Chelsea won 1-0 at champions Manchester United on Sunday to reclaim third place in the Premier League and tighten their grip on a Champions League place.A lacklustre game at Old Trafford was drifting towards a goalless draw when Mata collected a pass from Oscar and dispatched a low shot that took a slight deflection off Phil Jones on its way into the bottom-right corner.Mata's goal means that Chelsea will now go into Wednesday's crunch clash against Tottenham Hotspur at Stamford Bridge with a three-point lead over their London rivals, who are bidding to crash into the top four.Arsenal are sandwiched between the pair in fourth, a point behind Chelsea, having played a game more.United had right-back Rafael da Silva sent off late on and although their lead over second-place Manchester City remains 13 points, they have failed to win in two games since clinching their 20th league title.United made five changes from the side that drew 1-1 at Arsenal last weekend, with Rio Ferdinand, Wayne Rooney and goalkeeper David de Gea among the players dropping to the bench.Chelsea were missing Eden Hazard due to a calf strain and made four changes from their Europa League semifinal second leg success against FC Basle on Thursday.The visitors made a bright start, with United goalkeeper Anders Lindegaard touching a shot from Oscar onto the post and Demba Ba curling a shot wide from the left.