Summary Naomi Osaka beat Dominika Cibulkova 6-2, 6-1 to reach the Pan Pacific Open quarter-finals.
TOKYO (AFP) - 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.
