Not since 2012 has Serena Williams lost a match on red clay. The world No. 1 swept to her 26th consecutive win on what once was her least accomplished surface, brushing aside Carla Suarez Navarro in straight sets at the Mutua Madrilena Open. Suarez Navarro, a small Spanish clay specialist, arrived on a winning streak after earning her first career title in Portugal last week. She broke Serena's serve four times across two sets, a surprising rate considering her limited wingspan on return. But Suarez Navarro held serve just once in the match, never protecting her delivery long enough to make it a true contest.

Serena's next opponent can be expected to produce a more emphatic serving performance from her lanky frame. Former Wimbledon champion Petra Kvitova regrouped from three-set adventures in the first two rounds to record an impressively straightforward win over compatriot Lucie Safarova. The lower-ranked Czech had started the clay season with a bang by nearly upsetting Maria Sharapova in Stuttgart, and she had troubled Kvitova before. 

But rising above that hurdle merely positions Kvitova for a far more daunting task. She never has defeated Serena in five meetings, although they have not collided on clay. One of their two matches in 2013, however, might offer Kvitova some hope. The Czech forced Serena deep into a third set at Doha, even claiming a lead midway through that set, before the American collected herself to snatch victory from the jaws of defeat.

Whereas Serena never looked seriously threatened, world No. 2 Li Na needed to rally on Thursday from losing the first set to American No. 2 Sloane Stephens. Li took control over the second and third sets and closed out the match emphatically, but that lull recalled similar passages of wayward play at Indian Wells and mimai this spring. The reigning Australian Open champion shone when facing break points, however, saving nine of the 12 that Stephens earned whle converting four of her seven chances.

Li will need to maintain her strong first-serve percentage in the quarterfinals when she faces an opponent with an intriguing clay history against her. The Chinese star was the last woman other than Serena Williams to defeat Maria Sharapova on red clay. After winning their Roland Garros semifinal in 2011, though, she has lost a heartbreaker to the four-time major champion in the Rome final a year later and a somewhat routine match in the Stuttgart final last year. These two women now will have clashed at all four of the marquee clay events, not something that can be said of most key WTA matchups.

After she needed to rally against Christina McHale in the second round, Sharapova showed no sign of allowing the more dangerous Samantha Stosur to derail her. This opponent plays into the hands of a player as tall as the Russian, for the Aussie's kick serve and topspin groundstrokes create high bounces. Sharapova has dominated Stosur throughout their careers, and she dropped serve just once in another suffocating performance. Li will pose a thoroughly different test. The Chinese star is much more adept at counterpunching and covering the court albeit streakier and less intimidating on serve. 

One of the other Madrid quarterfinals will pit the normally clay-averse world No. 3 Agnieszka Radwanska against qualifier Caroline Garcia, the only unseeded player to reach this stage. Garcia upset 2012 Roland Garros finalist Sara Errani on Thursday and won a small clay title in Bogota this spring, so she should not be overlooked. Meanwhile, world No. 1 and 2008 Roland Garros champion Ana Ivanovic clashes for the second time this year with Simona Halep, having defeated the fast-rising world No. 5 on clay in Fed Cup. Ivanovic seeks her third consecutive semifinal at a WTA tournament, while Halep aims to remain in the hunt for her second marquee title of 2014 after winning Doha three months ago.