Chelsea striker Nicolas Anelka has warned the Blues must be at their defensive best to combat Barcelona's attacking instincts.The Londoners face Barca in the first leg of their Champions League semi-final on Tuesday night and Anelka is worried they about conceding an early goal.Guus Hiddink's side will be without suspended left-back Ashley Cole with Jose Bosingwa and Michael Mancienne among the candidates to keep flying winger Lionel Messi under control.Chelsea conceded four goals at home against Liverpool in the quarter-final second leg and were 2-0 down at half-time before fighting back to draw 4-4 and win 7-5 on aggregate. But Anelka is adamant that Chelsea cannot afford to be that sloppy in the Nou Camp.He said: "Against a team like Barcelona and the players they have, if we concede early goals it will be very difficult to come back, especially away from home, so as a team we will certainly have to be more focused on the defensive side of our game."The France international believes there will only be an advantage in the return leg at Stamford Bridge if they return from Spain with a good result."It is important to get a good result in the first match," said Anelka."If you lose that one by a big score the tie is almost finished. So it is very important for us to get something from the Nou Camp."If you want to win this trophy you know you will have to be able to beat a lot of very good teams."We have already beaten Juventus and Liverpool, who are both big sides, we know we can do it, so now we have to beat Barcelona."For the second successive season, there are three English sides in the last four of the competition and Anelka maintains that such consistency proves that the Barclays Premier League is the best in the world."It's the strongest league in the world," he added."Almost all the biggest stars in football play in England and that's why there are three English teams still in the competition."I think there is something special about playing in England and the Premier League is definitely something special."Fit-again Portugal international Bosingwa is favourite to play at left-back because of his experience at European level while goalkeeper Petr Cech looks to have come through his recent inconsistent spell.The Czech Republic international kept a clean sheet against Everton after conceding eight goals in his previous three matches.But he has received backing from Hiddink throughout and captain John Terry is another admirer of the 'keeper's qualities."For all those people who have had a pop at big Petr recently, just a reminder - we've let in fewer goals than any other Premier League team this season," Terry said."He will do for us. He is our mate and he's the best in the world and when he comes out in the last minute of a Wembley semi-final and gets through a crowd of players to punch the ball clear, we love him."