Wham-bam as Japan's Naomi Osaka blazes into Tokyo quarters

Alastair HIMMER
Osaka hits a return against Cibulkova

Japan's Naomi Osaka pulverised Slovak Dominika Cibulkova 6-2, 6-1 to reach the Pan Pacific Open quarter-finals on Wednesday in her first match since her historic US Open triumph.

The 20-year-old, who earlier this month stunned Serena Williams to become Japan's first grand slam singles champion, fired down 10 aces in a fearsome display of wham-bam tennis in Tokyo.

Third seed Osaka came out with guns blazing and ripped a fizzing forehand down the line on the first point, racing away to close out the first set with a pair of thundering aces.

A dazed Cibulkova, the 2014 Australian Open runner-up, had no answer to Osaka's firepower as the world number seven wrapped up a comfortable victory with a ferocious cross-court backhand after just 59 minutes.

"I didn't really feel any pressure -- I felt it was more fun," said Osaka, who reached the Tokyo final in 2016.

"I'm not really thinking about winning the US Open," added Japan's latest sporting celebrity, who has a Japanese mother and a Haitian father and was raised in the United States.

"I'm not sure what will happen when things calm down. But (today) as a whole I played at maybe 80 percent -- I never know the limit of what level I can go to."

Earlier, sixth seed Garbine Muguruza was upset by American qualifier Alison Riske 6-1, 6-2 in an abject performance from the Spanish former world number one, who looked a shadow of the player who captured the 2016 French Open and 2017 Wimbledon titles.

Riske advances to face fourth seed Karolina Pliskova, another player to have previously held the women's top ranking.

The Czech recovered from a set down to beat Australia's Daria Gavrilova 4-6, 6-4, 6-4 and avenge her opponent's defeat of twin sister Kristyna earlier this week.

But she made hard work of it, trashing a racquet in frustration as she slipped behind 4-1 in the deciding set before clawing her way back.

"The first set was in my hands but I made some stupid mistakes," said Pliskova, who ended Gavrilova's resistance with a clever drop volley after two hours and 21 minutes.

"I tried to stay positive and even though I broke my racquet I tried to keep fighting, because you always have a chance."

Second seed Caroline Garcia flirted with an early exit as the Frenchwoman overcame Russia's Anastasia Pavlyuchenkova 6-4, 2-6, 7-5 to reach the last eight of the prestigious Tokyo event, whose list of former champions includes Martina Navratilova, Steffi Graf, Kimiko Date and Martina Hingis.