BEIJING -- WTA Finals qualifiers Serena Williams, Maria Sharapova and Simona Halep confirmed their class with straight-sets victories at the China Open on Tuesday as two contenders to join them in the season-ending tournament suffered surprise defeats.
World No. 1 and defending champion Williams had struggled in her opening match on the blue hard courts of Beijing but the American was back to her best in her 6-2 6-3 second-round victory over Bulgaria's Tsvetana Pironkova.
The pair traded a break apiece in the first five games of the match before recently crowned U.S. Open champion Williams took control of the contest by reeling off three straight games to claim the opening set.
The second was a much tighter affair until Williams broke her opponent in a marathon ninth game and then held her own serve to secure victory in 74 minutes.
Like Williams, French Open champion Sharapova and Halep, runner-up at Roland Garros, are already assured of places in the eight-woman field at the WTA Finals, and they continued their good form on Tuesday.
Russian Sharapova produced some bruising groundstrokes as the world number four crushed Ukrainian Elina Svitolina 6-2 6-2 to set up a third-round meeting with Spain's Carla Suarez Navarro.
Romanian Halep had a slightly tougher time overcoming Chinese wildcard Zhu Lin 7-5 6-4.
World No. 167 Zhu followed Sharapova's aggressive tactics to move 5-4 ahead in the first set against second-ranked Halep, only to lose her composure and the match.
The Chinese produced 28 unforced errors as Halep's counter-punching approach helped her claim a win that sets up a third round clash with 15th seed Andrea Petkovic, the German having little trouble in ousting American Madison Keys 6-2 6-3.
The Beijing hard courts were not so welcoming for Canada's Eugenie Bouchard and Poland's Agnieszka Radwanska, however, with both continuing to struggle for late-season form as they look to add their names to the elite list in Singapore.
Bouchard, who lost in the final of last week's Wuhan Open, was beaten by unseeded German Sabine Lisicki 6-2 6-4, while Italian Roberta Vinci knocked out 2011 China Open winner Radwanska 6-4 6-4.
The defeats left the Polish world number six and seventh-ranked Bouchard still waiting to book a qualifying spot at next month's season-ending championships.
Former world No. 1, Serb Ana Ivanovic, who currently holds the eighth and final spot in the Race to Singapore standings, beat Swiss Romina Oprandi 6-4 6-2 on the Moon Court.
Venus Williams, seeded 16, also made the third round with a 6-4 6-3 victory over France's Caroline Garcia, while 13th-ranked Czech Lucie Safarova beat German Mona Barthel 6-3 6-3.