World No.1 Naomi Osaka powered her way into the quarterfinals of the Madrid Open with a 6-2, 6-3 win over Aliaksandra Sasnovich on Wednesday.

The top seed from Japan continued her impressive start to the clay court season, serving seven aces as she dispatched her 35th-ranked Belarusian opponent in 83 minutes.

Osaka, the reigning U.S. and Australian Open champion, showed greater focus after being pushed to three sets by Spaniard Sara Sorribes Tormo the previous day.

The 21-year-old, making just her second appearance in the main draw of the Madrid Open, will play in the quarterfinals for the first time.

In the men's draw, Japan's Kei Nishikori faced an unexpected battle in his second-round match against Bolivian Hugo Dellien, eventually prevailing 7-5, 7-5.

The world No. 7 served five aces and just one double fault in his first career meeting against Dellien.

The 109th-ranked South American came back from 5-1 down in the first set, pushing the 2014 finalist throughout the two-hour contest.