Chelsea defender Branislav Ivanovic has called on his team to be completely focused ahead of the big game against Manchester United Sunday at Stamford Bridge.

The Blues were far from impressive in the Champions League game against Shakhtar Donetsk Tuesday, going down 2-1, with most of the players failing to grasp the pace of the game.

United have a bad habit this season of conceding early goals, but have always found a way to come back, underlined by the 3-2 win over Braga in Europe, after they had fallen two goals behind with just 20 minutes gone.

With the attacking prowess at Sir Alex Ferguson's disposal, Ivanovic knows even the slightest slip-up will be punished by the likes of Wayne Rooney and Robin Van Persie.

"We need to improve our concentration and be focused on the whole 90 minutes," the Serbian international said.

"We conceded from the first chance (against Shakhtar) and it made it much more difficult for us afterwards to play the game we wanted. We have to analyse it and see where we can improve."

Chelsea's change is style this season has garnered much attention, with stylish playmakers Eden Hazard, Oscar and Juan Mata in particular shining for the Blues. However, with the attacking endeavour, the much-vaunted Blues defense has been left a bit exposed at times, and Ivanovic knows working together as a team - both defensively and in attack - will bear fruition against the bigger teams.

"This style is the change of the team and we defend like a team, and the same in attack," he said. "This has worked to our advantage and we must carry on but we have to stay compact in this kind of game, and make things easier for our team-mates.

"This is one of the crucial games for us this season, against Man United, with two difficult games before it. We have time to recover (after the Shakhtar loss) and do well, we know it's difficult to play against United and be we have to be focused for the whole 90 minutes if we want to win it."