Andre Villas-Boas believes Chelsea have ensured a "stressful'' Christmas for Manchester City and Manchester United by storming back into the Barclays Premier League title race.

The past three weeks have seen Villas-Boas' Blues almost halve what was a 12-point gap to leaders City, while victory at Wigan today will see them close to within just four points of top spot.

Chelsea's victory over City on Monday gave hope to all of the chasing pack, with United able to overhaul their Manchester rivals - temporarily at least - by winning at QPR on Sunday.

But Villas-Boas' side's success also put the top two on red alert that they may be about to produce the sort of run that saw them almost overcome a 16-point deficit to win last season's title.

"Nothing is going to be decided in December or January, but this is a stressful situation between the Manchester clubs,'' Villas-Boas said.

"So that gives us, the people chasing, the chance to shorten the distance.

"In four games in the Premier League, we reduced the distance by five points. We play Tottenham, we play Wigan, Aston Villa and Fulham.

"If we are able to shorten by another five points, it would be magnificent, but I wouldn't say that would happen.

"It's Man City-Arsenal being played this weekend and, again, this can have an influence on how the Premier League top four and five can look at the end of December.''

Villas-Boas knows his side must keep winning to maintain the pressure on City, who he is not expecting to go into meltdown after Monday's controversial loss at Stamford Bridge.

"It's not the first time that they've suffered defeat,'' he said.

"It's the first time in the league, of course, but it's not the first time that they've suffered a defeat this season and they've responded magnificently well.''

Victory would maintain Chelsea's 100% record since the start of the month, a run that has coincided with Villas-Boas abandoning his much-maligned high defensive line.

But he said: "Our defensive organisation was never, ever in question. High line or low line or whatever line, Liverpool are the best defence with 13 (conceded), then it's Man City with 15, and we are on 18.

"So I would say that we are pretty much a good defensive, solid organisation.''

So what does Villas-Boas believe is the secret behind Chelsea's resurgence?

"Confidence has a major boost - confidence, motivation,'' he said. "As you win, I think you solidify those processes.

"Hopefully, that is what is happening and we have to continue to perform, which is always difficult.''

The same applies in the Champions League following today's draw that paired Chelsea with Napoli, who effectively knocked City out of the competition.

The Blues will still be favourites to progress but not favourites for the competition, with Barcelona and Real Madrid hotly tipped.

But Villas-Boas, who won the Europa League with Porto last season, said: "It was funny because when I was at Porto, the Europa League favourites kept on changing as teams progressed or not.

"Eventually, a lot of big, big favourites fell out of the Europa League, from Man City, to Sevilla, to all of the Champions League teams apart from Benfica and Braga.

"That means at the moment there is a prediction but it doesn't mean that it's going to play right.''

Speaking before the draw was made, he added: "There's a big advantage to playing the second leg at home.

"This is the most gratifying thing of finishing first because it can stimulate your fans to create the right environment to help you get the result that you need to go through.

"If we manage to get this environment for the rest of the campaign, Premier League, or Champions League, or FA Cup, it'll certainly be a major help.''

Something else that would help Chelsea's chase for silverware would be the availability of Didier Drogba for as long as possible before the African Nations Cup.

City this week successfully negotiated for Yaya and Kolo Toure to link up with the Ivory Coast squad after their Carling Cup semi-final first leg against Liverpool.

That is 10 days before the African Nations Cup begins and Villas-Boas would like similar treatment for Drogba and Salomon Kalou, who he could be forced to release before Chelsea's FA Cup tie with Portsmouth three days earlier.

Asked if that was only fair, he said: "I would say so. I'm not sure if it's possible or not.''

Wigan boss Roberto Martinez is prepared to risk another 6-0 thrashing by Chelsea in search of a win.

The Londoners routed Martinez's men by that scoreline on their last visit to the DW Stadium in the second game of last season.

Wigan ultimately only avoided relegation from the Barclays Premier League on the final day of the campaign and they head into the home meeting with Chelsea again in deep trouble.

The Latics lifted themselves off the bottom of the table with victory at West Brom last week, but their Christmas schedule is tough with Liverpool and Manchester United coming next.

Martinez is determined to approach the festive programme positively, though, and said: "I just feel these games are great opportunities for us to try to get something where nobody expects us to.

"I don't like to go into a game thinking about it being damage limitation or just trying to get through unnoticed.

"It is a unique opportunity to go and try to express yourself and test yourself to the maximum.

"That means sometimes that will leave you exposed and you could end up on the end of a difficult scoreline but I think we need to be prepared to do that.

"I think the only way you can get a positive result against the top sides is if you take risks.

"You need to score goals and that is the only way you can do that.

"I would rather give everything we've got and be heavily challenged and see what the outcome is.

"If you look back, we had a heavy defeat with Chelsea at home and then we had a victory.

"I would rather that than losing both games by minimal scorelines."

Martinez is not fazed by the prospect of facing Chelsea at a time when they have started to find their form.

Their manager Villas-Boas had found himself under pressure after a difficult start to the campaign, but the past fortnight has seen that change.

Martinez said: "After the performance at West Brom - and the manner we had to get those three points where we were heavily tested in every aspect of our game - I just feel we are ready to go and compete with one of the top teams in the league and a team that probably have turned their season around.

"They have had two unbelievable moments in their season, qualifying for the knockout stages of the Champions League and then being the first team to beat the impressive Manchester City this season.

"So, we know they are going to be on top of their moment of form but we are ready to be ourselves and enjoy a good footballing day."

Having won at Sunderland and West Brom in recent weeks, Martinez now wants to make the most of home advantage, with Liverpool also visiting the DW Stadium next Wednesday.

The Spaniard feels confidence has been restored after a run of eight successive defeats with seven points having been collected in the last four games.

Martinez said: "You have to be perfect in your performances against the top sides and I feel you can do that playing at home.

"You have the support of the fans, you have the real belief that something special can happen.

"We have been disappointed with the points we dropped in the first third of the competition but for the first time in five years we got back-to-back away wins, which is a really difficult feat to achieve in this league.

"That has given us a real feelgood factor and in many ways we feel ready to start our season.

"We know we have got a difficult challenge in the next three games, they are going to be a big test, but there is a really good feeling in the dressing room."