The Blues needed Frank Lampard's 79th-minute penalty to beat bottom club Portsmouth at Stamford Bridge; Pompey's French striker Frederic Piquionne had earlier cancelled out a first-half opener by compatriot Nicolas Anelka.
A penalty was also pivotal at Turf Moor, where Burnley held Arsenal 1-1 on Wednesday night. Cesc Fabregas gave the Gunners an early lead, only for Graham Alexander to level from the spot in the 28th minute. Arsene Wenger's men are now five points behind United but still with a game in hand.
Tottenham are just two points further adrift following a comprehensive 3-0 home win over Manchester City. Goals from Niko Kranjcar (2) and Jermain Defoe inflicted only the visitors' second loss of the season - their first since the 4-3 derby defeat to United.
Liverpool climbed to sixth place after surviving a late scare at Anfield. Jason