Halep, Kvitova through to China Open quarters

BEIJING (AP) Rafael Nadal is back in form on the tennis court - and in his sharp-tongued critiques of the ATP tour. The second-seeded Spaniard reached his

BEIJING (AP) Rafael Nadal is back in form on the tennis court - and in his sharp-tongued critiques of the ATP tour.

The second-seeded Spaniard reached his first quarterfinal since capturing his record ninth French Open title in June with a 6-3, 6-4 win over German qualifier Peter Gojowczyk at the China Open on Thursday, then blasted the choice of tennis balls at the tournament.

''The ball is so bad here,'' Nadal said. ''If you throw the ball on the floor, the bounce goes everywhere. Is not a question of winning or losing. I won in Rio (earlier this year) with this ball. I won tournaments with this ball.

''It's just that we're competing at the top level of our sport, tennis, and the ball is an important thing.''

The 14-time major winner has complained previously about the ball in question - manufactured by Head - but he also criticized the decision to switch ball manufacturers from tournament to tournament, saying it could result in injuries.

''This week we are playing with one ball. Next week we are playing with a different ball,'' he said. ''That's dangerous for the shoulder, dangerous for the elbow.''

The Spaniard wasn't nearly as critical of his own game in his second match back from a two-month layoff due to a right wrist injury.

He was sharp for much of the match until the final game when he double-faulted and made two unforced errors to give Gojowczyk three break points. He fought them off, however, and closed it out on his fourth match point.

Nadal faces another qualifier in the quarterfinals, Martin Klizan, who advanced when seventh-seeded Ernests Gulbis of Latvia retired with a shoulder injury while trailing 6-2, 3-0.

In the women's draw, Simona Halep of Romania also withdrew from the tournament with a left hip injury immediately after winning a back-and-forth match against Andrea Petkovic of Germany 7-6 (4), 5-7, 7-6 (1).

The second-seeded Halep took a medical timeout for treatment on her hip after the first set, but returned to complete the match, which featured 17 breaks of serve and 105 combined unforced errors (61 from the Romanian).

''It was a tough match against Andrea today, and I had to fight a lot. I'm happy I was able to win and finish the match in the right way, but I have a hip injury and it would be risky for me to play again tomorrow,'' Halep said in a statement.

Halep's withdrawal gave ninth-seeded Ana Ivanovic of Serbia a pass to the semifinals. The 2008 French Open champion, who is fighting for a spot in the WTA finals in Singapore, earlier beat Sabine Lisicki of Germany 6-3, 7-5.

Two-time Wimbledon champion Petra Kvitova also advanced when Venus Williams withdrew before their match with a viral illness.

Venus' sister, Serena, retired from a match last week at the Wuhan Open, citing a virus, as well. Serena Williams, the China Open's defending champion, will play Lucie Safarova for a spot in the quarterfinals later Thursday.

Two other seeded players were knocked out of the tournament, shaking up the race for the WTA finals in Singapore.

Seventh-seeded Angelique Kerber of Germany was defeated by two-time major winner Svetlana Kuznetsova 2-6, 6-4, 6-3, while No. 12-seeded Ekaterina Makarova of Russia fell to Roberta Vinci of Italy 6-1, 0-6, 7-5.

Because of those losses, Eugenie Bouchard of Canada and Agnieszka Radwanska of Poland, both of whom lost early in Beijing, are assured of making the eight-woman field in Singapore.

Other men's winners included sixth-seeded Andy Murray, who defeated Pablo Cuevas of Uruguay 6-2, 6-2, and third-seeded Tomas Berdych.