Barcelona coach Pep Guardiola talks up influence of Javier Mascherano ahead of Chelsea semi-final

Argentine has unexpectedly been answer to Barça's defensive crisis and has also stepped up in the dressing room

When Barcelona gave up on signing Cesc Fabregas in 2010, they went out and brought Javier Mascherano. It felt like a consolation prize for their supporters, who had missed out on the jackpot. Instead of the jewel in Arsenal's crown, this was a cog in the Liverpool machine. An important cog, and an intelligent player good enough to become a success at Barcelona, but not the prodigal son who would come home a year later.

Fabregas scored on his league debut, Mascherano was taken off at half-time on his, yet as both players prepare for tonight's tie at Stamford Bridge it is Mascherano's name that will go down first on Pep Guardiola's teamsheet.

"He has been the key," said the coach when talking about Barça's recent run of 10 straight league wins. The £20m signing who looked like expensive back-up for the holding midfielder Sergi Busquets has become the team's most important defender. Underlining his exceptional moment of form he has played every minute of the last three games, without committing a single foul.

Dani Alves believes Mascherano will go on to become a top manager and Juan Mata, who will face him tonight, singles him out as the pick of Barcelona's defenders ahead of his own Spain team-mates Carles Puyol and Gerard Pique.

Asked about taking on fellow Spain internationals Pique, Puyol and Victor Valdes, Mata said: "Victor is a fantastic goalkeeper and Barcelona are a great team who defend as well as they attack but there is a player who is fundamental in that – Mascherano. He has been incredible this season."

Alves was asked to identify the Barcelona player he thought was most likely to go on to become a top coach. Expecting Xavi or Puyol to be the Brazilian's choice, he said: "Mascherano. Whenever I talk to him, he tells me something new. It's incredible how he reads the game. He notices things that others don't."

His reinvention as a central defender has been the key to his success under Guardiola. Comparing him to Eric Abidal, the coach said: "He has that same high level of concentration." The news that Abidal would need a liver transplant, bringing his season and almost definitely his career to an abrupt and sad end, has made Barça's need even greater and Mascherano has stepped up both on and off the pitch.

A dressing room that had to digest Abidal's relapse, while slipping 10 points behind Real Madrid in the league and with Guardiola publicly uncommitted to staying, has needed leaders. Despite most of his team-mates having years on him in time spent at the club, Mascherano has provided that leadership.

The start to his Barcelona career was far less explosive than Fabregas's. He was substituted at half-time as Barça lost 2-0 at home to newly promoted Hercules in 2010, but his coach always believed that the climb to acceptance was well within him. He finally planted his flag on the summit with that incredible last-ditch tackle on Nicklas Bendtner late on in the Champions League quarter-final against Arsenal last season and has been imperious ever since.

Fabregas's fortunes have worked in reverse. The former Arsenal captain made an incredible start, scoring almost all his 15 goals in the first half of the season. He has failed to find the net in the league since January and has not scored in any competition since February.

Last night Fabregas admitted he was happy with his first year at Barcelona. He said: "I have played much more than I expected. And this is why I joined – for weeks like this. This is the biggest week of the season with a semi-final and the game against Real Madrid, which if we win will put us right back in the title race. It's my first year but I am more than happy with the way it has gone.

"Games against Chelsea have always been the same for me. You can dominate the game and then with their first counter-attack [Didier] Drogba scores against you. It's the same story so many times.

"With [Andre] Villas-Boas they tried to have more possession but now they have gone back to the Chelsea of old with the tactics that made them so successful before playing on the counter-attack, looking to hit Drogba when they can."

He was also asked about watching Barcelona's dramatic win over Chelsea in 2009 when still an Arsenal player: "I remember seeing the goal, watching the match with my family, and just as we had decided to turn off the telly and put the PlayStation on the ball went in and we celebrated."

He will be watching from the sidelines again tonight if Guardiola believes Seydou Keita's physical presence is more important than the goal threat of his summer signing. There are no regrets from Barcelona about bringing him back and he may yet have a decisive say in their challenge for three trophies. But it is Mascherano in the ascendant.

Nicknamed "el jefecito" he is not just the "little chief" any more, he's Barça's little chief. "I wouldn't swap him for anybody," Guardiola said recently. And, for the moment, that includes Fabregas.

Chelsea duo's jinx

Neither Javier Mascherano nor Cesc Fabregas have enjoyed much success against Chelsea. Former Liverpool midfielder Mascherano won three of 10 matches against them while with the Reds, while Fabregas fared worse, winning three of 16 Arsenal games against Chelsea.

Mascherano record v Chelsea P10 W3 D3 L4; Goals 0, Bookings 4.

Fabregas record v Chelsea P16 W3 D4 L9; Goals 2, Bookings 7.