China's Zhu Lin staved off a spirited mid-match comeback to upset Petra Kvitova for her first top-20 victory in the opening round of the Tianjin Open on Wednesday.

The unseeded 23-year-old from Wuxi, Jiangsu province, beat the two-time Wimbledon champion 6-4, 5-7, 6-4, then followed up by beating Hsieh Su-wei of Chinese Taipei 6-3, 6-1 on Thursday.

Kvitova was the first to blink in her first meeting with Zhu, handing her rival the chance to break at 4-4.

The Czech former world No 1, now ranked 17th, missed out on a break in the next game as her unforced error count crept up.

Zhu ran up a 5-4 lead in the second set and appeared on course for a comfortable win before Kvitova produced a flurry of winners to take the contest to a third set.

However, world No 113 Zhu went on the attack, taking a 5-3 lead in the decider. She had two chances to seal the match on Kvitova's serve before eventually prevailing.

"I played so relaxed today," Zhu said.

"In the second set I was serving for the match, but she played great to win this, and then I came back in the third set and I played like my first set - and I did it!

"I just played my match. I didn't think too much about the win, I just enjoyed the match."

Maria Sharapova made an impressive start to the Tianjin Open on Wednesday by beating Romania's Irina-Camelia Begu in straight sets.

Seeded ninth, Begu loomed as a tricky first-round opponent for Sharapova, but the former world No 1 from Russia swept to a 6-4, 6-2 victory.

Currently ranked 86th after returning from a 15-month doping ban, Sharapova - granted a wildcard in Tianjin - plays unseeded Magda Linette of Poland next.

The 30-year-old Sharapova, who returned to tennis in April after serving a suspension for taking the banned substance meldonium, has yet to win a tournament since then.

The five-time Grand Slam champion exited the China Open last week in the third round at the hands of Romania's Simona Halep, the newly crowned world No 1.

But Sharapova had no such trouble against Begu, seeing off the 57th-ranked Romanian in 82 minutes.

The opening matches of the Tianjin Open have been badly disrupted by rain and Sharapova said she was glad to finally get into action.

"It's been a long wait for everyone, it hasn't been easy," the Russian told the WTA website.

"I had a first practice outdoors and then I think it rained for 70 hours straight, unfortunately for the players."

Venus falls

Elsewhere, Venus Williams was stunned in the second round of the WTA Hong Kong Open on Wednesday, losing 7-5, 6-2 to Japanese teenager Naomi Osaka.

Osaka, ranked No 1 in her homeland, reeled off eight consecutive games at one stage to power into the quarterfinals.

It all seemed to be going to plan for second seed Williams when she broke the 19-year-old Osaka in the fifth game of the opening set.

But then the American's first serve deserted her when serving for the set at 5-4.

Two double faults and some fierce Osaka ground strokes that kissed the lines enabled the world No 64 to break twice and take the set 7-5.

"She played well," said 37-year-old Williams, a seven-time Grand Slam winner.

"You know, I made a few errors at 5-4 and after that she played pretty flawless. I can only give her credit for playing so well."

Osaka, who knocked defending champion Angelique Kerber out of the US Open last month, then raced into a 5-0 second-set lead.

"I felt like I played offensively and hit really deep, hard balls, but she had the luck today and could return those balls even harder and deeper," said Williams.

Williams briefly rallied to 5-2, but, after a pep talk from Osaka's coach, the Japanese closed out the match on her serve at the second time of asking.

"Venus is someone I've respected and admired," said Osaka, who was not born when Williams reached her first Grand Slam final at the 1997 US Open.

"I've grown up watching her. Even though she is someone I admire, it's just another opponent at the end of the day so I tried to focus hard."

Reuters - AFP