John Terry's own goal blew the race for the title wide open once again as Crystal Palace snatched an unlikely win at Selhurst Park.
The former England defender turned Joel Ward's 52nd-minute cross into his own net under pressure from Joe Ledley to hand the Eagles a precious 1-0 home win and boost Manchester City and Liverpool's hopes of reining in the leaders.
It was no more than Palace deserved from a performance of real character and endeavour on a day when Jose Mourinho's men were far from at their best.
Victory lifted Tony Pulis' side one place to 16th, but crucially five points clear of the drop zone.
It proved to be a good day too for beleaguered Manchester United manager David Moyes as a Wayne Rooney double helped to lift some of the pressure from his shoulders.
On a day when a group of disgruntled fans chartered a plane to display the message "Wrong One - Moyes out", Rooney cancelled out Ashley Westwood's fine 11th-minute free-kick with a deft header and then fired United into the lead from the penalty spot after Juan Mata had been felled.
Mata's first goal for the club gave the home side breathing space and substitute Javier Hernandez wrapped up a 4-1 win at the death.
United remain in seventh place in the table, but Southampton continued their pursuit with a comprehensive victory over Newcastle which saw them leapfrog the Magpies into eighth.
The Saints had to wait until stoppage time at the end of the first half to take the lead after being repeatedly thwarted by keeper Rob Elliot, standing in for the injured Tim Krul.
However, once Jay Rodriguez had opened the scoring there was no way back for Alan Pardew's men as fellow England World Cup hopefuls Rickie Lambert and Adam Lallana helped themselves to a goal apiece before Rodriguez sealed victory at the death with his second.
But perhaps the game of the day took place at the Hawthorns as West Brom and Cardiff fought out a six-goal thriller.
The Baggies looked to be cruising to victory when they went 2-0 up within nine minutes of the kick-off after Morgan Amalfitano floated an outrageous second-minute opener over goalkeeper David Marshall before Graham Dorrans extended their advantage.
However, the Bluebirds dragged themselves back into the game on the half-hour through Jordon Mutch's strike, and levelled 17 minutes from time when defender Steven Caulker powered home a header from Gary Medel's free-kick.
But there was still drama to come when Thievy Bifouma looked to have snatched victory for the home side three minutes into added time, only for Mats Daehli to deny them with virtually the last kick of the game.
South Wales neighbours Swansea enjoyed a much more comfortable afternoon as they eased to a 3-0 victory over Norwich which left the Canaries looking anxiously over their shoulder once again.
Jonathan de Guzman's first-half double laid the foundation with Wayne Routledge's second-half strike completing the job.
Peter Odemwingie's fourth goal in three appearances for Stoke was enough to see off Hull as the Potters reached the 40-point mark.