BARCELONA - Treble-chasing Barcelona face their biggest challenge yet when they face Guus Hiddink's rejuvenated Chelsea in the Champions League semifinal first leg in Barcelona tonight.

BARCELONA - Treble-chasing Barcelona face their biggest challenge yet when they face Guus Hiddink's rejuvenated Chelsea in the Champions League semifinal first leg in Barcelona tonight.

Pep Guardiola's players sent out a warning with the way they tore apart Bayern Munich in their first leg match in the last round with Lionel Messi leading the charge but ably assisted by Thierry Henry and Samuel Eto'o in the three-pronged attack.

They now face a far tougher challenge from an in-form Chelsea side who may realistically be out of their domestic championship race, but beat Arsenal to reach the FA Cup final and are in the Champions League semifinal thanks to two spectacular games against Liverpool.

The biggest threat is set to come from Chelsea's physical strength, and Barcelona are especially wary of the danger they pose from set-plays.

Chelsea's Ivory Coast striker Salomon Kalou believes today represents a tough assignment, but could be a classic encounter.

"These are the types of games everyone wants to play in. It's going to be really hard but we have the team to beat anyone," said Kalou, who is desperate to reach a second successive final after losing to Manchester United on penalties last year.

As well as the Champions League last four, Barcelona are in the Copa del Rey final and well-placed to win the league despite only managing a draw against Valencia at the weekend.

It will be a crucial two weeks for the Catalan giants.

In La Liga, they will play the 'El Clasico' against second-placed Real Madrid, who are four points off the top, in between the Chelsea games.

"We are physically and mentally prepared for Chelsea and we must make sure that they don't score an away goal," warned Barcelona midfielder Xavi Hernandez.

Both teams go into the match having rested key players. - Sapa-AFP