United head to Stamford Bridge looking for the win that would allow them to leapfrog their hosts and regain the Premier League's top spot.

For them to succeed in that quest, Ferguson knows there must be no repeat of the shoddy defending that saw them concede three goals against CSKA Moscow this week that nearly ended their 23-match unbeaten home record in European combat.

The return of Nemanja Vidic from a calf injury should help, even if Rio Ferdinand's continued absence is starting to cause concern.

In any case, Ferguson is convinced his defenders will respond to the challenge Chelsea will undoubtedly pose.

"We won't be as open as we were on Tuesday," vowed the United chief.

"In a way, we experimented a little bit and it didn't particularly work.

"But I know we are capable of getting back to the form we showed last season because we are a team with great ability."

If there was experimentation, it could only have been with young teenager Fabio Da Silva given the rest of United's back four were internationals.

Some of the sharpness has been missing throughout the campaign, a fact suspended skipper Gary Neville puts down to the constant changes Ferguson has had to make.

The United manager is not so sure. After all, on their record-breaking 14-match run of Premier League clean sheets last term, Ferguson had to make changes on a pretty regular basis.

In fact, looking back, he now feels the Club World Cup, a competition he was so wary of, played a major part.

"The challenge of having to go to Japan focused all our minds," he said.

"We needed to get results before we went to Japan and we needed to get results afterwards because we were games and points behind teams.

"The players buckled down to the job and produced some terrific performances."

Indeed, Ferguson is not being overly critical now. He nominated Wes Brown and Jonny Evans as two of his better players on Tuesday, even though the central defensive unit was exposed.

With Vidic returning, Ferguson must now decide which man remains to try and quell the threat of Didier Drogba.

While admitted what a handful the Ivorian can be, the United boss reserved most of his praise for Chelsea's driving force Frank Lampard, who has managed to maintain a high level of consistency despite playing in the vast majority of matches for the Blues.

"Lampard still retains a fantastic energy to come down the pitch," he said.

"Looking at his statistics and appearances it is quite an exceptional record for a midfield player. He obviously looks after himself.

"Chelsea have an exceptional player in that respect and very good experience in the rest of the team, which can be important."

After a couple of turbulent years, Chelsea certainly seem to have benefited from the stability Guus Hiddink brought during his brief reign at Stamford Bridge.

Although Hiddink returned to his full-time job with Russia in the summer, Carlo Ancelotti has enjoyed a virtually seamless transition, which in itself is some achievement given his only previous knowledge of the English game came as an opponent, both player and manager.

He has remained loyal to his trusted diamond formation though, which the Chelsea players have responded to.

Joe Cole's return to fitness has proved greater balance on the left and, overall, Ferguson is quite impressed.

"When you change a manager you change the philosophy of the team too," he said. "New physios come in, new coaches and a new manager with new ideas.

"Ancelotti had the diamond formula for years. It was unlikely he was ever going to change that.

"The job has been to mould the team to his vision."

The admiration needs to be set aside though. United have not won at Stamford Bridge since 2002 and after defeats at Burnley and Liverpool, the run needs to change.

"We have to get our act together because our record down there has not been good for the last six years," said Ferguson.

"It is a strange situation because we used to have a terrific record down there up until a few years ago. But we have let it slip.

"The players all realise it is going to be a big game and their performance is going to be important."