Eden Hazard's 38th-minute goal has put Chelsea on course for a victory over Manchester Untied which would end their opponents' slim Premier League title hopes.
The PFA Player of the Year favourite got the better of fellow nominee David de Gea towards the end of a first half in which United had previously enjoyed the better moments.
The Red Devils have won their last six top-flight games to move within eight points of the leaders and started brightly as Luke Shaw's perfect cutback set up Wayne Rooney for a left-footed shot which bent just wide of the post.
Ander Herrera and Paddy McNair, recalled in defence in one of several changes enforced on Louis van Gaal by injury, shot wide from distance as United's bright start continued while Chelsea struggled to make an impression.
Cesc Fabregas got into a couple of promising positions for the Blues only to be snuffed out by Herrera and Marouane Fellaini, and the Spaniard played a role in a wonderfully-worked team move which cut the visitors open for the goal.
After John Terry had forcefully dispossessed Radamel Falcao on the halfway line, Fabregas passed into Oscar's feet and, with his back to goal, the Brazilian back-heeled into the path of Hazard, who ran clear of the defence and tucked through De Gea's legs for his 18th of the season.
Should Jose Mourinho's side see out the victory at Stamford Bridge, they would only need eight points from their remaining six matches to guarantee a first title since 2009-10.
