Chelsea keeper Petr Cech has warned his team-mates to stem the tide of goals flowing past him at the start of games and after half-time intervals.
Chelsea fell behind to Shakhtar Donetsk just three minutes into their Champions League game on Tuesday night and ultimately fell to their first defeat of the season, denting the confidence of Roberto Di Matteo's squad ahead of Sunday's showdown with Manchester United at Stamford Bridge.
The Blues also failed to shoot out of the blocks as they conceded two quick goals to Tottenham at the start of the second half in last weekend's Premier League game at White Hart Lane and Cech believes a lack of concentration may be to blame for Chelsea's struggles to get up to speed with a game.
"Shakhtar are a pure counter-attacking team and we allowed them to score in the third minute," he told the Chelsea website. "This had a huge impact in the game because when we had possession and lost it they had the chance to counter, to shoot, to finish.
"They have been doing really well and we gave them a huge lift in the third minute, then we saw them play with the confidence.
"We started slowly like we did in the second half against Tottenham and we got punished for that. We have to make sure we start games better than this. If you are unlucky and someone scores goals, you can't control this, but we have lacked a little concentration."
Cech has suggested the shock of losing in the Ukraine may be a good wake-up call for Chelsea ahead of their date with Sir Alex Ferguson's men.
"In a way what happened against Shakhtar was a good experience for us because we have to defend better," he added. "We played well when we have the ball but not when we didn't have it.
"If you do this against Manchester United, you are in big danger because they are the same type of team, playing on the counter-attack away from home. Hopefully it was a good lesson and we learn for the weekend."