Saturday's El Clasico between Real Madrid and Barcelona at the Bernabeu could be the deciding act in the La Liga title race this year.

Spain's two most powerful clubs are locked at the top of the table for a month, since Barca were held 2-2 in Almeria and relinquished first place to their arch-rivals on goal difference.

The champions travel to face the leaders tied on 77 points with eight matches left to play, a massive 21 points ahead of third-placed Valencia after steamrollering most of their opposition this year.

Real are on a 12-match winning streak in the league and have won all their home matches, while Barca have lost only once all season, which makes the second 'Clasico' all the more significant.

As the two teams brace up for what is being billed the 'Game of the Millennium', here's five head-to-head battles to watch out in Saturday's potentially decisive match.

Iker Casillas v Victor Valdes

Spain captain Iker Casillas' position as first-choice goalkeeper for Vicente del Bosque at the World Cup finals is not in doubt, but he has not looked so assured recently, making some uncharacteristic errors.

Barcelona's Victor Valdes won the 'Zamora' award for the best record in La Liga last year and tops the charts again going into the 'Clasico'.

Like Casillas, Valdes is an excellent shot-stopper and his distribution from the back is the starting point for Barca's suffocating possession game.

Calls for the uncapped Valdes to go to South Africa as third-choice behind Casillas and Pepe Reina will increase if he outshines his opposite number on Saturday.

Xabi Alonso v Xavi

Spain midfielder Xavi makes Barcelona tick even if he doesn't necessarily dominate the headlines.

His slick link-up play is the very essence of Barca's style, and cutting the distribution lines from the diminutive playmaker is vital to breaking Barca's domination of the ball.

Xabi Alonso plays a similar role at Real, though has had less time to settle into the role.

He's a stronger physical presence and conducts affairs from a deeper lying position, but is often the starting point for Real's swift counter-attacks.

Gonzalo Higuain v Lionel Messi

If club form was anything to go by Argentina would be unstoppable at the World Cup finals with the goals of Higuain and Messi.

They top the La Liga goalscoring charts with 24 and 26 respectively, but while Messi's goal-scoring feats are hailed around the world, Higuain's contribution at Real is under the microscope.

The 22-year-old's gutsy displays have helped Real perform many of their trademark comebacks, flourishing in broken play with his surging runs into the area.

But he has gone missing in big games, where he has been let down by poor tactical awareness and a profligacy in front of goal.

He has, however, the perfect stage to prove his doubters wrong by stealing the limelight from perennial headline-maker Messi.

Cristiano Ronaldo v Zlatan Ibrahimovic

Ronaldo cost Real just over 90 million euros last summer, and Ibrahimovic moved to Barcelona in a deal worth around 60 million euros.

It's hard to judge the commercial impact of the respective signings on their clubs, but on the field of play the towering Swedish striker has gone closer to repaying some of the investment than his flashy Portuguese rival so far.

Ibrahimovic scored the game's only goal when Real visited Barcelona in November while Ronaldo missed his best chance when denied in a one-on-one with Valdes.

The former Inter Milan striker scored valuable away goals against Stuttgart and Arsenal in the Champions League to help Barca into the semi-finals.

Real slumped out of the competition to Olympique Lyon in large part due to their failure to score in France when they lost 1-0, though Ronaldo did open the scoring in the 1-1 draw at the Bernabeu.

Ibrahimovic has netted 15 in the league and Ronaldo 18. Should the sides finish level at the end of the campaign their head-to-head record will decide the title.

Manuel Pellegrini v Pep Guardiola

Pep Guardiola has an impressive three 'Clasico' wins from three attempts and could survive a defeat at the Bernabeu.

His side are hitting their stride for the critical part of the campaign and received a boost in morale with their progress to the Champions League semi-finals on Tuesday.

He hardly ever changes the way his team plays and lets opponents worry how to get the ball from his players.

Manuel Pellegrini experimented with tactics and personnel during his first season at the helm, and it isn't immediately clear which is his best side.

They often win games from moments of inspiration by key players. They are lethal on the counter-attack which will be their main weapon against ball-hungry Barca.

A victory followed by the league title, the only silverware left for him, could help preserve Pellegrini's position into next year after disappointments in Europe and the domestic cup.