Jose Mourinho's Blues have taken a 10-point lead over the rest of the competition after defeating Louis van Gaal's Red Devils 1-0 at Stamford Bridge thanks to Eden Hazard's 38th-minute goal.
United's loss ended a six-game winning streak in the league and although they managed to stay in third position, they saw their lead over fourth cut to just one point by neighbours Manchester City.
The reigning champions recorded their first win in three outings with a 2-0 result over West Ham United at home Sunday courtesy of a James Collins own-goal which came prior to Sergio Aguero's 20th league strike of the campaign.
Nigel Pearson's Foxes were served by Leonardo Ulloa's first league goal since Boxing Day and Andy King's second in third outings to move up to 18th on the table where they now sit equal with Hull City who are in the safety zone.
In other Premier League matches over the weekend, West Bromwich Albion scored a crucial 2-0 victory over Crystal Palace at Selhurst Park to move eight points clear of the bottom three. James Morrison and Craig Gardner were on target for the Baggies.
Brilliant strikes from Mame Biram Diouf and Charlie Adam allowed Stoke City to get the better of Southampton 2-1 at the Britannia to move up to ninth while Tottenham returned to the winners' list in impressive style with a 3-1 victory at Newcastle United.
Nacer Chadli, Christian Eriksen and Harry Kane all hit the back of the net for Spurs - the latter getting his 30th of the season in all competitions - while Jack Colback scored for the Magpies who have now lost six matches in a row to fall to 14th.
2014/15 Barclays Premier League - season scores