Manchester United beat QPR 2-0 on Saturday © Getty Images Enlarge

Manchester City manager Roberto Mancini believes cross-town rivals Manchester United are lucky to be 15-points clear at the top of the Premier League.

Mancini was forced to rue another Red Devils victory as the league leaders outclassed Queens Park Rangers 2-0 at Loftus Road on Saturday - their fourth victory in a row extending the lead over second-placed City.

But as his side prepares to face Chelsea at home on Sunday, a belligerent Mancini claims it is only luck that has proved the difference between the top two clubs this season, luck which could very quickly run dry.

"Until now United were lucky with everything. They won a lot of games in the last minutes," Mancini told the Sun. "If United go forward in the Champions League the last two months will be hard for them.

"They could lose five points in two games before the derby."

But before the two clubs clash again at Old Trafford in April, Mancini and his men must overcome the "tough challenge" of Chelsea to peg back United's substantial lead.

Despite a topsy-turvy season, Chelsea still hold third spot on the ladder, four points behind City, and will be looking to capitalise on any disconsolation felt around the Etihad Stadium.

But City midfielder Yaya Toure said he and his team-mates were well aware of what was needed to reel in the gap to United, revelling in the opportunity to begin the fightback against the reigning European champions.

"It will be a tough, tough game because Chelsea are close to us," Toure said. "It's very important to keep close to United. I love the big games. The key games are the ones against the big clubs - Chelsea, United, Tottenham, Liverpool. Chelsea are not an easy team to beat - we know that.

"If we are not to let United get even further away we have to keep working hard and win."

And the 29-year-old Ivory Coast international issued a warning to the Red Devils, saying City will never give up in the fight to become the dominant force in the Eastlands.

"We know United are a great club but we are becoming a great club and we will never stop fighting," he said. "Manchester City want to become one of the world's big clubs and to achieve that level we have to start from the beginning. It is part of sport [having to win] and pressure from the press is part of sport. It's a great enjoyment to be part of a top team that is trying to achieve something.

"Since I came to City I enjoy my football more because my football is all about more attack. I want to stay longer."

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