Chelsea midfielder Michael Ballack believes the Blues have a 50-50 chance against Champions League semi-final opponents Barcelona.The Blues booked their place in the last four of Europe's elite competition after a remarkable 7-5 aggregate victory over Liverpool.Barca, meanwhile, are the bookmakers' favourites to claim glory in Rome's final, having easily disposed of Bayern Munich in their quarter-final tie.Ballack, though, is confident ahead of the encounter, expressing his belief that his team-mates will be buoyed by their Liverpool scalp.The German told Sky Sports: "Everybody knows about the strength of Barcelona, you could see it in the quarter-final against Bayern Munich, especially in the first leg when they scored four goals."So we know what to expect. I think our chances our 50-50. We are a strong team. We won against Liverpool and that gives us a lot of confidence."Blues midfielder Lampard also expects a stern test when they face Barca, but is also optimistic of his side's chances.He said: "(It will be) very tough. Everyone is tough now, but probably no one more so than them."They have got some outstanding individuals and probably the best player in the world in (Lionel) Messi."If we get our minds right and prepare right then we have a chance."