Alex Ferguson has admitted Manchester United face a far tougher task overhauling Chelsea in the Premiership title race than they did with their successful pursuit of Arsenal two years ago.

As United famously dragged back the Gunners' eight-point lead in the final 10 games of that campaign, Ferguson claimed his eighth league championship would go down as one of the finest achievements of his managerial career.

But as the games tick by this term with Chelsea looking increasingly unlikely to suffer the blip both Ferguson and Arsene Wenger have predicted, the Scot acknowledges the 11-point lead Jose Mourinho's side holds over his will be much more difficult to overturn.

"This is a mammoth task, far tougher than the one we faced two seasons ago," said Ferguson. "Chelsea are not showing any sign of slipping at all. We keep hoping they will have a blip but at the moment it doesn't look as though it will happen.

"You have to acknowledge their form has been brilliant but, football being what it is, you just never know."

Given the state of the title picture, Ferguson has not been able to take any solace from knowing victory over Aston Villa today will take United above Arsenal into second spot, their highest position of a season that has improved markedly from what could turn out to be a title-breaking start of just one win from the first five games.

Of far more importance to Ferguson is a run of fixtures over the next 13 days which also includes Wednesday's English League Cup return with Chelsea, the FA Cup encounter with Middlesbrough and the much-hyped Highbury clash with Arsenal.

"These are exciting times," he smiled. "We have some massive games coming up, the type every player wants to be involved in.

"We are in championship-winning form at the moment and the momentum that has given us should carry the players into this period with great confidence."

Meanwhile, Mourinho has revealed how attempts by Ferguson and Wenger to undermine Chelsea's title challenge had backfired.

The Chelsea chief insists the volley of pre-Christmas comments had precisely the opposite effect to what was intended. He claimed the remarks only served to heighten Chelsea's motivation during their crucial festive fixtures.

Ferguson claimed that Chelsea would struggle to claim points in the north, but Mourinho's side answered that jibe by achieving a notable victory over Liverpool at Anfield.

Chelsea went unbeaten through their four festive period games without conceding a goal.

"The big secret was the pressure that some tried to put on us and the way that the team wanted to show we are not worried by that pressure, and we are ready to cope with it," Mourinho said.

"Everyone was thinking of a 'blip', or at least that we would lose some points, but we didn't. We just won four consecutive matches.

"The four games in 10 days are always dangerous. We showed game after game that we are strong mentally and I think that our direct opponents were not expecting that.

"As we showed we were strong enough, I think they lost a bit of their confidence and motivation.

"But as I said to the players, when you are top of the league, you can make a mistake. Because you can make a mistake, you have no pressure. And if you have no pressure, normally you don't make mistakes. So we had a good chance to play cool.

"The Liverpool and Portsmouth games were good examples of that, just waiting for the right moment to score.

"The players were magnificent to play two away games with just 24 hours' rest and to spend New Year's Eve in the hotel, just speaking on the phone with their families."