Updated

Flushing Meadows, NY (SportsNetwork.com) - Five-time champion Serena Williams, Wimbledon titlist Petra Kvitova and two-time Big Apple runner-up Victoria Azarenka eased into the third round, while eighth seed Ana Ivanovic was a second-round upset victim Thursday at the U.S. Open.

CiCi Bellis, the first 15-year-old since 1996 to win a U.S. Open match, could not follow that up with another victory, losing in the second round to Zarina Diyas of Kazakhstan.

Diyas claimed a 6-3, 0-6, 6-2 victory over Bellis, who stunned 12th-seeded Aussie Open runner-up Dominika Cibulkova on Tuesday. That made Bellis the youngest player to win a U.S. Open match since Anna Kournikova in 1996.

"I mean, I think just playing, you know, my first U.S. Open and just having, you know, that under my belt, then it will be easier, you know, the next time I play," said Bellis.

The world No. 1 and two-time reigning U.S. Open titlist Williams flattened fellow American Vania King 6-1, 6-0 in 56 minutes at Ashe Stadium on another sun-drenched day in New York.

Williams' third-round opponent will be a third straight compatriot, Varvara Lepchenko, who eased past German Mona Barthel 6-4, 6-0. The 17-time Grand Slam champ Williams whipped fellow countrywoman Taylor Townsend on Tuesday.

The third-seeded Kvitova won her ninth straight Grand Slam match by pasting fellow Czech Petra Cetkovska 6-4, 6-2.

The hot left-hander Kvitova is fresh off her title in New Haven last week and captured her second Wimbledon title last month. Her next opponent will be Serb Aleksandra Krunic, who took out 27th-seeded American Madison Keys 7-6 (7-4), 2-6, 7-5.

Canadian Eugenie Bouchard, the No. 7 seed, outlasted Sorana Cirstea of Romania 6-2, 6-7 (4-7), 6-4.

Bouchard is through to the third round here for the first time in her career. She appeared in at least the semifinals at this year's first three Grand Slam events, including a runner-up finish at Wimbledon.

Meanwhile, 42nd-ranked big-hitting tall Czech Karolina Pliskova stunned the former world No. 1 from Serbia Ivanovic 7-5, 6-4, while the 16th-seeded former top-ranked star Azarenka handled American Christina McHale 6-3, 6-2 on the grounds at the USTA Billie Jean King National Tennis Center.

Having her best season since 2008, Ivanovic is a former French Open champ who has only ever reached one U.S. Open quarterfinal. She joined fourth-seeded Agnieszka Radwanska as another top-10 second-round upset victim over the last two days.

Ivanovic leads the WTA with 48 match wins this season.

The two-time Australian Open titlist Azarenka appeared in the last two U.S. Open finals, losing to the incomparable Williams both times. The Belarusian star is still on the mend after missing three months of action this year due to a foot injury.

"Christina started really well, not missing a ball, and I felt like I was always on my back foot," Azarenka said in a post-match interview after beating McHale. "I tried to fight and got my momentum, and felt like I started to do what I should have been doing in the beginning."

Up next for Azarenka will be Russian Elena Vesnina, who slipped past New Zealand's Marina Erakovic 7-5, 2-6, 6-4.

Eleventh-seeded Italian Flavia Pennetta dismissed American Shelby Rogers 6-4, 6-3 to set-up a match with another American, Nicole Gibbs, who upset 23rd- seeded Russian Anastasia Pavlyuchenkova 6-4, 6-7 (6-8), 6-3, while 15th-seeded Spaniard Carla Suarez Navarro spanked American Coco Vandeweghe 6-3, 6-3.

A former U.S. Open champion was sent packing when Estonian Kaia Kanepi cut down 24th-seeded Aussie Samantha Stosur 3-6, 6-3, 7-6 (10-8). Stosur stunned Serena in the final here three years ago.

In other action involving seeds, No. 17 Russian Ekaterina Makarova routed Slovenian Polona Hercog 6-1, 6-2, No. 29 Aussie Casey Dellacqua overcame China's Wang Qiang 4-6, 6-4, 6-2 and No. 30 Czech Barbora Zahlavova Strycova came back to best Romanian Monica Niculescu 4-6, 6-4, 6-2.