Serena Williams brushed aside Maria Sharapova 6-1 6-3 to advance to the Madrid Masters tennis semi-finals along with top-ranked Victoria Azarenka on Friday. Williams sealed her seventh straight win over Sharapova with an emphatic slam on the new blue claycourt. Earlier in the Spanish capital, Azarenka overcame a shaky start to beat French Open winner Li Na 3-6 6-3 6-3. Williams opened strongly, hitting six aces and earning two early breaks to take the first set against the second-ranked Russian. Sharapova finally showed some fight and broke for love to even the score at 2-2 in the second set, but she quickly squandered her break with a costly sixth double fault to fall behind for good. Williams, who improved to 11-0 on clay this year, will face US Open champion Sam Stosur or Czech Lucie Hradecka. After Azarenka struggled on serve early on, last year’s runner-up found her stride and broke her Chinese opponent’s first two service games of the second set en route to pulling even at a set each. Azarenka, who has won four titles this season, then used her powerful groundstrokes to jump out to an insurmountable 4-0 lead in the decider before holding off Li’s late charge. “There are a lot of things that I had to change and come up with in order to surprise her because she was pretty unbelievable in the first set,” said Azarenka. “I had to turn something around. I don’t know if it was confidence or if it was self belief or just pushing myself to be better and really wanting to win the match.” Azarenka also said she agrees with Rafael Nadal and Novak Djokovic in their criticism of the court’s new surface that was changed from red to blue clay. “I do agree that it is very slippery. You feel unstable sometimes, actually, a lot of times,” she said. “But right now, there is no point on talking about it. After the tournament, all the players can get together and discuss it.” The Belarusian will next face fourth-seeded Agnieszka Radwanska of Poland, who beat American Varvara Lepchenko 6-4 6-4. On the men’s side, Argentina’s Juan Martin del Potro hit 10 aces to beat Alexandr Dolgopolov of Ukraine 6-3 6-4 and set up a semi-final with Tomas Berdych. The sixth-seeded Berdych defeated Fernando Verdasco 6-1 6-2. The Spaniard made 24 unforced errors and showed little of the flare on display on Thursday when he ousted Rafael Nadal. Top-ranked Djokovic will face countryman Janko Tipsarevic and Roger Federer will play David Ferrer later on Friday.