Azarenka dispatched Andrea Hlavackova 6-3 7-6 and Sharapova saw off Klara Zakopalova 6-4 6-3.

Sharapova, who beat world number one Azarenka in the Stuttgart final last month, was first up on the unfamiliar blue clay of the Manolo Santana show court, a controversial innovation at this year's edition of the event that has prompted mixed reactions from players.

With the sliding roof closed to keep off the morning drizzle, the Russian soon found her range and broke Zakopalova's serve in the opening game.

The three-times grand-slam singles champion wobbled when serving for the match at 5-2 in the second set but broke again in the next game for a comfortable win that set up a meeting with another Czech, unseeded Lucie Safarova, or Spanish wildcard Carla Suarez Navarro.

Sharapova said the blue clay was a little more slippery than its red counterpart but that she generally approved of the decision to switch colours, which organisers argue makes it easier to follow the yellow balls on television.

"I did feel a bit of a difference with the amount of clay that is on the court and the bounces were a bit off, especially the first couple of days of practice, but I feel like it's gotten better and settled in a little bit," she told a news conference.

"You just have to work on your balance a bit more," added the 25-year-old world number two, who will be chasing the only grand slam that eludes her at the French Open starting later this month.

Belarussian Azarenka had newly-appointed adviser Amelie Mauresmo watching from her box alongside coach Sam Sumyk and made short work of Hlavackova, who needed treatment on a problematic left thigh midway through the second set.

Like Sharapova, Azarenka missed a chance to serve out the match in the second set but went on to take the tiebreak 7-2 and will next play Russian Nadia Petrova or Ana Ivanovic of Serbia, a former world number one who is seeded 13.

"It is a little bit slippery but it's the same for everybody," Azarenka told a news conference when asked about the blue court.

"I don't like to complain about the surface, it is what it is," the Australian Open champion added.

"You have to deal with it and nobody's going to change it now so everybody is playing in the same conditions."

Serena Williams, seeded nine and making her first European appearance of the season, plays unseeded Russian Anastasia Pavlyuchenkova later on Tuesday, a day after her sister Venus was knocked out by Germany's Angelique Kerber.

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