Real Madrid President Florentino Perez poached the flamboyant Portuguese, a Barca assistant coach in the late 1990s, from Inter Milan at the end of the 2009/10 season to try to wrest the Spanish title back from the Catalan capital.
The consensus, at least among the Madrid fans, is that Real are closer than ever to matching the team many consider the best club side ever and several hundred million TV viewers worldwide will tune in for kick-off to witness the latest installment of one of the most intense rivalries in the game.
Real's form ahead of the clash that could go a long way to deciding the title has been hugely impressive.
They have won their last 10 league games - and their last 15 in all competitions, equalling a club record - and lead Barca by three points with roughly a third of the season played and with a game in hand.
"You never know in football, there are always surprises," Mourinho, who has a habit of rattling his former club, said after Real's 3-0 Champions League victory at Ajax Amsterdam on Wednesday.
"But right now we feel more confident and we are a better team than last season," added the former Chelsea manager.
Pep Guardiola's side, chasing a club record-equalling fourth consecutive domestic title, have been almost impeccable at their Nou Camp stadium in La Liga, winning eight and drawing one and scoring 39 goals without reply.
However, they have managed only two victories in six away games, scoring eight and conceding seven.
Playmaker Xavi said on Wednesday that statistics were meaningless once the players took to the field and unexpected events can, and quite often do, change the game in a moment.
Recent 'Clasicos' have included several mass brawls and a slew of red cards, as well as some outstanding individual performances.
"It's true that Madrid are in good shape," Xavi, who heads to Japan next week with his team mates for the Club World Cup, told a news conference.
"They are a bit better but that does not mean anything," added the Spain international, who will make his 600th appearance for Barca if selected on Saturday.
"The 'Clasicos' have nothing to do with statistics and anything can happen."
Guardiola has enjoyed the upper hand over Real since the former Barca and Spain midfielder took over as coach at the end of the 2007/08 season.
He has engineered victories in seven out of 11 'Clasicos' and after Mourinho arrived at Real, when their rivalry grew yet more intense, he has three wins, three draws and only one defeat, in the King's Cup final in April, Mourinho's only silverware in his first season at the helm.
Saturday's game will match up not only two of the game's most influential coaches, but also the world's two best players.
Argentina forward Lionel Messi an
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