Part four of a five-part series gets underway on Wednesday when rivals Real Madrid host Barcelona at Santiago Bernabeu in the first leg of the Champions League semi-final.

The two La Liga giants met three times earlier over two competitions.

First, the Catalans went a 5-0 thrashing of Real Madrid at Camp Nou, in late November. David Villa scored twice in a humiliating loss for Los Galacticos, and things got very testy when Cristiano Ronaldo pushed Barcelona manager Pep Guardiola.

The La Liga rematch just 10 days ago featured two converted penalty kicks by perhaps the two best players in the world: Lionel Messi and Cristiano Ronaldo. The 1-1 result almost seemed like a moral victory for Real Madrid after the November result.

Then there was last week's Copa del Rey Final. In a classic match that went to overtime, Angel Di Maria's cross that sailed into the box for a Ronaldo header was the difference, as Real Madrid was able to hold on for their first Copa del Rey title since 1993.

Now, the two face off again. This time, the stakes are a trip to the Champions League Final to play either Manchester United or Schalke 04.

Guardiola's side faces a long list of injuries. Defenders Maxwell, Adriano, and Eric Abidal will be sidelined while Carles Puyol is uncertain to start. Forward Bojan Krkic is out as well, but defender Gabriel Milito is expected to be available.

Jose Mourinho's squad is less hobbled. Only Sami Khedira is injured, though Ricardo Carvalho is out due to suspension.

Real Madrid will likely try to duplicate their performance in the Copa del Rey by trying to play an ugly style and counter-attack. Mourinho has no problem conceding style points in favor of a victory.

The difference in Wednesday's match might be Messi. The star forward was not very visible in the Copa del Rey Final and didn't score in the 5-0 Barcelona victory. Messi's only goal in three matches against Real Madrid was a penalty, and he will certainly like to change that.

For Real Madrid, this would also be an opportunity for Ronaldo to gain ground in the race for the Ballon d'Or. The Portuguese star won the European Football of the Year honors in 2008, but finished second to Messi in 2009, and didn't finish in the top three as the Argentine won the FIFA Player of the Year Award in 2010.

Another great performance from Ronaldo could be the only way to beat Barcelona. The Catalans will have a chip on their shoulders to avenge the Copa del Rey loss, and to beat their rivals.

Real Madrid know they need a win. The second leg will be in Camp Nou, and everyone remembers how the last match turned out.

Expect another physical match, and plenty of dives. That would benefit Real Madrid, as Ronaldo wants to set up free-kick situations.

Barcelona will continue to attack, and probably don't mind that that plays into the hands of Real Madrid. The more Barcelona pushes, the more vulnerable they will be should they turn the ball over. With an injured defense, Guardiola needs to instill in his players that Real Madrid's attack needs to get frustrated by the midfield.

A tie of any kind would be a good result for Barcelona, but judging by the way they've dominated opponents this season, Barcelona has a win on their minds.

Manchester United Real Madrid Lionel Messi Real Madrid