(CNN) -- Manchester United slumped to their second successive Premier League defeat to throw the English title race wide open on Saturday.
Danny Murphy (right) is congratulated by teammates after scoring the opener from the spot at Craven Cottage.
The reigning champions went down 2-0 to mid-table Fulham and ended with nine men after Paul Scholes and Wayne Rooney were sent off at Craven Cottage.
Defeat for the leaders follows their calamitous 4-1 home reverse to arch-rivals Liverpool last week.
United remain four points clear of Chelsea, who were beaten 1-0 by resurgent Tottenham Hotspur at White Hart Lane.
Liverpool can cut the gap to just a single point with victory over Aston Villa on Sunday, but would have played a game more.
United made a sorry start when Scholes was sent off for the eighth time in his career, raising both hands to block Bobby Zamora's header from a corner.
Danny Murphy put away the 18th minute penalty and the home side kept United on the back foot for the rest of the half as Zamora went close with two more chances.
United piled on the pressure after the break with Cristiano Ronaldo and Ji-Sung Park wasting chances from close range and finding Mark Schwarzer in unbeatable form in the Fulham goal.
With United pressing forward, Zoltan Gera finished them off with an acrobatic second in the 87th minute.
Rooney then needlessly collected a second booking to be sent off with a minute to go to complete a dismal afternoon for United.
Manager Alex Ferguson acknowledged their recent poor run could wreck their season.
"If you lose games in March and April it can cost you," he told Press Association.
"Fortunately we have a slender lead at the moment but not a lot and I'm hoping we come back from the internationals back to our best."
Tottenham's victory over Chelsea was some consolation for United, who still have a game in hand on Guus Hiddink's men.
After a first half stalemate, Luka Modric put Tottenham ahead in the 50th minute as he drove home a ball cut back by the excellent Aaron Lennon.
The Croatian went close from a similar position after being set up by Lennon, but Chelsea finished the game strongly with home keeper Heurelho Gomes making several fine saves, keeping John Terry out with an acrobatic effort.
Brazliian defender Alex also hit the top of the crossbar with a header in a frantic finish.
It was the first defeat for interim boss Hiddink since he took over at Stamford Bridge.
"When you're chasing you have to win your games but to lose the goal as we did in the 10 minutes after half-time, with so many professionals and internationals, is bad for us," Hiddink told Sky Sports News.
"You have to know, when there is a fire in the kitchen, when to flood that fire."
Earlier, Portsmouth boosted their fight against relegation as two goals from Peter Crouch gave them a 2-1 win over sixth-placed Everton.
Fellow strugglers Blackburn were held 1-1 at home to West Ham, with bottom club West Brom drawing 1-1 with Bolton.
Stoke's 1-0 home win over Middlesbrough, who remain in the drop zone, could prove a crucial result with Ryan Shawcross scoring six minutes from time.
Saturday's late game saw Arsenal step up their bid for the fourth Champions League spot with a 3-1 win at Newcastle, who slip into the bottom three.
Obafemi Martins, who failed to convert a first half penalty, made amends with a swift equalizer after Nicklas Bendtner headed Arsenal ahead in the 57th minute.
But with key home defender Steven Taylor receiving treatment, Abou Diaby put Arsenal ahead again after exchange of passes with Robin van Persie who also set up Samir Nasri for the clinching third at St James' Park.