BEIJING (AFP) - Former world No. 1 Maria Sharapova qualified for the quarter-finals of the Shenzhen WTA on Wednesday (Jan 2) after struggling against China's great tennis hope Wang Xinyu, who was forced to retire from the match in pain.

The fifth-seeded Russian was surprised early on by the power of her 17-year-old opponent, who won the first set 7-6 and broke in the second.

But Wang was forced to retire while leading 5-2 in the second set, apparently after feeling pain in her thigh.

"You played unbelievable," Sharapova told Wang, after the Chinese player announced she was retiring from the match, adding that the teenager had a great career ahead of her.

"It's not the way either of us wants to finish the match, win or lose," added Sharapova, who is ranked 29th.

"I thought (Wang) was absolutely the dominant player in this match, and had all the opportunities to win it, even though I felt like I was finding my stride and getting a little bit closer to the line and being more aggressive."

Wang won two junior doubles titles last year at two Grand Slam tournaments (Wimbledon and Australian Open).

She was given a wild card for the tournament in Shenzhen.

In the next round, Sharapova takes on top-seeded Belarusian Aryna Sabalenka, who had an easy 6-3, 6-3 win over Russian Ekaterina Alexandrova on Wednesday.