Chelsea midfielder Frank Lampard admits they're underdogs in their Champions League semifinal clash with Barcelona.

"We have to look back at the mistakes we make as a group in conceding goals. We have to be strong and we need to tighten up defensively," he said.

"If we are going to beat Barcelona we need to play at the level we achieved in the first leg against Liverpool when we won 3-1.

"It will be a very tough game because of the way they're playing, but we know what to expect, particularly in the away leg.

"Barcelona are probably favourites at the moment because of the way they're playing, but being favourites doesn't mean you go through.

"Barcelona are the form team in Europe, if not the world. They've been like that all season so there can't be a tougher match for us in this competition."