U.S. Open champ Osaka eases to victory on return to action in Tokyo

Osaka, who stunned Serena Williams to become Japan's first grand slam singles champion earlier this month, produced another display of fearless power-hitting to put away Slovak Cibulkova in just under an hour.

(Reuters)

The 20-year-old, cheered by the capacity home crowd, raced into a 4-0 lead in the opening set and then went on break her opponent three times in the second to ease to victory.

"It was really difficult," third-seeded Osaka said courtside. "I'm just grateful that I could play in front of you guys."

Osaka will either play Barbora Strycova of the Czech Republic or Estonia's Anett Kontaveit in the quarter-finals.

Earlier in the day, two-time Grand Slam champion Garbine Muguruza suffered a shock 6-1 6-2 defeat by American qualifier Alison Riske.

World number 75 Riske scored her third victory over a top-20 ranked opponent this year, recording 19 winners to just nine unforced errors.

In her fifth quarter-final of the season, Riske will next face fourth seed Czech Karolina Pliskova.

(Reporting by Hardik Vyas in Bengaluru; Editing by Christian Radnedge)