Serena Williams (USA)  vs Dominika Cibulkova (SVK) .mSerena Williams got revenge on Gabine Muguruza in a hard-fought 2-6 6-3 6-2 win that was a lot closer than the score indicates. Cibulkova, last year's surprise finalist here, played what most observers are calling the best match of the tournament to date in her win over 2-time Australian Open champion Vika Azarenka, coming down from a break in the final set to prevail, 6-2 3-6 6-3. Interestingly, it was Cibulkova who took more risks and went for more when the stakes were raised in that contest, which served her well when her main weapon, the forehand down the line, spanking the line. . Serena has never lost to the hard-hitting pint-sized dynamo, and after being forced to raise her game against Muguruza, I'm confident she will be ready to dispatch the Slovak. Mad Professah's Pick: Williams in 2 sets.
Venus Williams (USA) 
Ekaterina Makarova (RUS)  vs Simona Halep (ROU) . Makarova always playes her best tennis in Ausatralia, having earned a lot of big scalps down under (as both Williams sisters know).In the last year, Makarova has been starting to make her presence felt at the other majors as well, with a semifinal berth at the 2014 US Open. Her lefty spin and excellent movement can be a devastating combination, now that she has the belief that she can hang out there with the elite of the game. Her mental toughness will be tested in the extreme against the resiliency of Simona Halep, however, who generally wins the matches she is supposed to win and rarely loses to people lower ranked than she is. Mad Professah's pick: Halep in 3 sets.
Eugenie Bouchard (CAN)  vs Maria Sharapova (RUS) . Again, this match-up between the two closest ranked opponents in the Final 8 should make for the most compelling tennis but when you look at their head-to-head record Sharapova has won all three meetings, although their semifinal match at the 2014 French Open was one that really could have gone either way, and Bouchard is well aware of that. Sharapova knows that she is playing with house money having survived 2 match points in the 2nd round against unheralded Russian Alexandra Panova while Bouchard has let the pressure of expectations lead to complications when she was closing out huge leads against players she would be expected to beat. Mad Professah's pick: Sharapova in 3 sets.