SHENZHEN • If Naomi Osaka was suffering from "first-round jitters" en route to her win over Petra Kvitova, then her tenacity in getting through the three-set marathon must surely place her among the favourites for the WTA Finals title.

The in-form Japanese yesterday outlasted her Czech opponent 7-6 (7-1), 4-6, 6-4 in two hours and 39 minutes for her maiden victory at the season-ending tournament.

Despite several nervy stretches, Osaka, 22, opened the US$14 million (S$19 million) round-robin tennis event in the same way she has played the other two events on the Asian swing.

Having claimed titles in Osaka and Beijing, the world No. 3 stretched her winning streak to 11 matches, equalling her best career run set last year starting with her US Open triumph.

In a rematch of this year's Australian Open final, the Czech world No. 6 came out with intent, but Osaka held off two break points before clinching the tiebreak. It seemed to shake Kvitova's confidence but the oldest player in the draw at 29 clawed back in the second set.

A refocused Osaka, however, put her foot down in the deciding set before finally closing it out in the 10th to issue a statement to her rivals in the Red Group.

After maintaining her unbeaten record over Kvitova, having won their other clash in Melbourne, the former world No. 1 said: "You can't really afford it (to be nervous) here. I tried to fight no matter what and I'm very glad I was able to win.

"I didn't play well in the Finals last year, so I'm kind of just trying to redeem myself a little bit in that sense."

In the later match, top-ranked Ashleigh Barty of Australia beat Swiss Belinda Bencic 5-7, 6-1, 6-2, with the win also securing her world No. 1 status for the year.

She came back from a torrid first set marred by 20 unforced errors and an inability to crack her opponent's confident serve.

But the French Open champion rediscovered her consistency with a blistering second set, breaking the world No. 7 twice and levelling the match with an ace.

Bencic, 22, had to receive medical treatment on her left heel after the second set, leaving her hampered for the remainder of the one-sided match, but Barty still felt it had been a tough test.

"To play against the best of the best, every match is high quality," the 23-year-old said. "It's about coming out here and bringing the best each time."

In the Purple Group, world No. 2 Karolina Pliskova plays defending champion Elina Svitolina, while US Open champion Bianca Andreescu takes on Wimbledon winner Simona Halep today.

AGENCE FRANCE-PRESSE