TOKYO (Reuters) - U.S. Open champion Naomi Osaka continued to flourish in front of her home crowd at the Pan Pacific Open in Tokyo, as she comfortably dispatched Barbora Strycova 6-3 6-4 on Friday to reach the semi-finals.

The 20-year-old is competing at her first event since winning her debut Grand Slam earlier this month and looks to have brought her New York form home with her as she has yet to drop a set so far in Tokyo.

Osaka proved too powerful for Strycova from the off, storming into a 4-1 lead in the first set with a dominant service game, while her forehand was too strong for the world number 25 to handle.

Despite some crafty defense from Strycova to stay in the contest, the result never appeared in doubt as Osaka won easily in one hour and 35 minutes.

The Czech beat Osaka when the two met three years ago in Tokyo but Japan’s first ever Grand Slam winner is a very different proposition now and Friday’s win was her ninth in a row.

Osaka will face Italian Camila Giorgi in the semis on Saturday after Victoria Azarenka was forced to retire injured in their quarter-final contest with Giorgi leading 5-3 in the first set.

Osaka and Giorgi have never faced each other before in WTA competition.

Earlier in the day, fans at the Tachikawa Tachihi Arena were treated to a marathon contest that saw Karolina Pliskova defeat Alison Riske, the conqueror of two-time Grand Slam winner Garbine Muguruza earlier in the tournament, 6-1 6-7(5) 7-6(4) after over two and a half hours of play.

Pliskova, who went out in the quarter-finals in Tokyo last year, twice came from a break down and saved two match points in a thrilling final set to outlast the American qualifier and set up a semi-final meeting with Donna Vekic.

Croatian Vekic shocked world number four and second seed Caroline Garcia 6-3 6-4 to continue her unlikely run at this event.

The unseeded 22-year-old broke Garcia five times on route to a comfortable victory, her first over the Frenchwoman.

Vekic is hoping to secure her first ever WTA Premier level title in Tokyo, while former number one Pliskova is looking to reach her second final of the year.