Seven months ago, Mourinho ended Barcelona's Champions League campaign when his Inter Milan team held on to complete a semi-final victory over the then holders before going on to lift the trophy at Madrid's Santiago Bernabeu stadium.
The colourful Portuguese was immediately hired by Real with a mission to re-establish the club as Spain's pre-eminent power and the results so far have been spectacular.
Unbeaten in all competitions, Real lead La Liga having won 10 and drawn two but Barca remain just a point behind. After a relatively slow start they looked close to their brilliant best in an 8-0 win away to Almeria last weekend.
Pep Guardiola's side followed that up by thumping Panathinaikos 3-0 in the Champions League to secure a place in the last 16 as group winners. They have scored 33 goals in their 12 league games, conceding just eight.
Real, who swept aside Ajax Amsterdam 4-0 on Tuesday with a double from La Liga top scorer Cristiano Ronaldo, have netted 33 league goals and conceded only six under Mourinho, who got his big break as a translator for Bobby Robson during the Briton's stint as Barcelona coach before going on to win the Champions League with Porto and Inter.
It is still early in the season, of course, but a game that will be watched by millions worldwide could have a huge bearing on a title battle that was only ever going to involve two teams.
Real failed to win the league last season mainly because they lost both games to Barca, stretching their losing streak against Guardiola's team to four.
WORLD'S BEST
Monday's game will match up not only two of the game's most influential coaches, but also the world's two best players.
Former World Player of the Year Ronaldo has put together an incredible run of goals for Real since the start of October, scoring 17 in 12 matches.
Current World Player Lionel Messi is also on a hot streak. Barca's Argentina forward scored his sixth goal of this season's Champions League in Athens and has 13 league goals, one short of Ronaldo.
The assertion by Barca midfielder Xavi that his side are the favourites is backed up by the bookmakers' odds, which just favour a home victory.
"It's an important match and we are favourites because we are playing at home," Xavi told reporters in Athens. "We are playing well and on good form."
However, Ronaldo said the arrival of Mourinho and players including Mesut Ozil and Ricardo Carvalho had revolutionised the side.
"The 'Clasico' will be very interesting because Madrid this year is completely different than last year," said Ronaldo, who became the world's most expensive player when he joined from Manchester United at the end of the 2008/09 season.
"We are in a good moment and we believe in ourselves so I think we're going to win there," the Portuguese added, in an interview with Castrol Football.
DISTANT THIRD
