With their wins in the semifinals, both players reached milestones. For Sharapova, it was her 19th consecutive clay court win and 500th WTA tour win. For Serena it was her 30th win of the year (compared to only two losses, to Sloane Stephens in the Australian Open quarterfinals and to Victoria Azarenka in the Doha final).
This is Serena's first red clay final since she won the Roland Garros title in 2002, Sharapova is the defending French Open champion and has won three other red clay court titles in the last two years (Stuttgart 2012, Stuttgart 2013, Rome 2012). Serena won the title here last year when it was played on "controversial" blue clay. In fact, she beat Sharapova handily on that surface (while I watched delightedly from the stands) 6-1 6-3. If she wins, Serena will become the 10th player in history to win 50 WTA Tour titles (49-16 in finals) while Sharapova would win her 30th (29-20 in finals).
Sharapova must have gained confidence with how she played the first 75 minutes of her match against Serena but the fact that she has lost their last 10 consecutive meetings must still prey on her mind. Serena has not been playing her best tennis at all in Madrid, while Sharapova appears to be happy on and off the court. In fact, in the quarterfinals Annabel Medina Garrigues became only the 6th player to ever win a bagel set from Serena and led 4-2, 30-all in the final set before succumbing 6-3 0-6 7-5. So, Serena will be definitely taking the occasion of playing her arch-nemesis on a surface which she has had limited success very seriously. It should be an interesting preview of what we'll be seeing in Paris in a few weeks. (Another interesting question will be if either one will withdraw from the Rome tournament, which Sharapova won last year and Serena reached the semifinals, depending on the result of this final. If Serena loses, then she would have to just reach the Rome final to regain the World #1, but she might have to go through Venus Williams to do so. If Sharapova withdraws she will almost certainly be ceding the #1 ranking to Serena for the French Open.)
MadProfessah's prediction: Serena in 3 sets.