Ferguson's side are now nine points ahead of second placed Chelsea after Ronaldo hit his 16th goal of the season with just two minutes remaining at Craven Cottage.

"We scored so late on, it could be significant," Ferguson said. "We are in a fantastic position but we have some difficult away games left.

"Liverpool will be hard for us next week. I am not saying we are going to win but I know for certain we will not play as badly."

United had fallen behind when Brian McBride took advantage of a mix-up between goalkeeper Edwin van der Sar and Nemanja Vidic to fire home after 17 minutes.

Ryan Giggs equalised in the 29th minute when he volleyed past Jan Lastuvka from Wayne Rooney's cross.

It took until the 88th minute for a below-par United to snatch the winner when Ronaldo's surging run and shot, which deflected off Philippe Christanval, sparked wild celebrations among Ferguson and his players.

Ferguson added: "Ronaldo was fantastic and showed courage. I don't know how many times he was fouled, but he kept going and he deserved man of the match and the goal."

Chelsea have a game in hand on United, but they could be 12 points behind by the time they play their next league match at Portsmouth on Saturday as the leaders face Liverpool earlier the same day.

Charlton boss Alan Pardew told his players not to let their standards slip after they boosted their survival bid with a 4-0 rout of his former club West Ham.

Pardew was sacked by the Hammers in December and replaced by former Charlton boss Alan Curbishley.

But a Jerome Thomas double and goals from Darren Ambrose and Darren Bent gave him a measure of revenge as they closed the gap on fourth bottom Wigan to three points.

Pardew said: "The performance was good but today the win was all-important no matter how it came. We've set our standards for the rest of the season with this win.

"It's been a difficult day, a difficult week leading up to it for me because I have a genuine love for West Ham and their fans which will never die."

Curbishley has won just one league game since taking over but he was given a vote of confidence after the match when West Ham issued a statement saying his job was safe.

Curbishley said: "I'm as devastated as the fans are. We are getting problems time and again but West Ham were losing games before I came and I just haven't been able to change it.

"The question is are we going down with a fight or a whimper? There are still 10 games left, lots of points at stake. The first thing would be to get a settled side and a result."

Sheffield United manager Neil Warnock accused Steven Gerrard of diving to win the penalties that set up Liverpool's 4-0 win over the Blades at Anfield.

The Liverpool captain earned two first half spot-kicks that were converted by Robbie Fowler, before Sami Hyypia and Gerrard scored to complete the rout.

Warnock said: "I told him I was disappointed with him. He was looking at the referee Steve Bennett, almost asking for the penalty.

"Some referees would see that Steven Gerrard used everything he had to get the penalty.

"Steve Bennett just rules by the laws of the game, he says that is consistency. He needs to understand the game more."

Australia striker Mark Viduka scored Middlesbrough's opener and made their second in a 2-1 home win against Reading.

Gareth Southgate's side went ahead after seven minutes when Emanuel Pogatetz flicked on Stewart Downing's cross and Viduka pounced to score with a smart back-heel from close range.

Viduka was involved again when he played in Yakubu and the Nigerian smashed a fierce shot past Marcus Hahnemann. John Oster's 87th minute goal for Reading was too little too late.

Watford missed a chance to climb off the bottom of the table when they were beaten 3-0 by Everton at Vicarage Road.

Manuel Fernandes gave Everton the lead in the 23rd minute before Andrew Johnson increased Everton's advantage two minutes later with a penalty. Leon Osman's superb stoppage time strike made in three.