World No. 1 Victoria Azarenka and former top-ranked stars Maria Sharapova and Venus Williams were second-round winners Tuesday at the 2012 Olympic Tennis Event.

Azarenka celebrated her 23rd birthday by taking care of Spanish left-hander Maria Jose Martinez Sanchez 6-1, 6-2 on Court 2 at the All England Club.

"It was a special moment to have a birthday during the Olympic Games but unfortunately I cannot really celebrate as I have to get ready for tomorrow," Azarenka said.

Azarenka has spent most of 2012 at No. 1 after capturing her first-ever major title at the Australian Open back in January.

Up next for the Belarusian slugger will be Russia's Nadia Petrova on Wednesday.

The third-seeded former world No. 1 Sharapova got past game 18-year-old British left-hander Laura Robson 7-6 (7-5), 6-3 under the roof on Centre Court at the All England Club, where rain delayed play on the outside courts earlier in the day.

Sharapova was asked about the atmosphere at the Olympics compared to Wimbledon.

"Oh, I love it. Obviously, you felt it so much today, playing against someone that's from Great Britain," Sharapova said. "You feel the support that the home country's providing to the athletes. What a transition it has been from the last few weeks of Wimbledon to here, a nice one, a completely different atmosphere which I think all of us are really enjoying.

"It's much more of a team atmosphere as well. The girls are getting together in the evenings, having dinner together, which has been nice."

Sharapova needs an Olympic gold medal to complete a career "Golden Slam." She secured a career Grand Slam by capturing her first-ever French Open title last month.

The 25-year-old superstar's third-round opponent on Day 5 will be 15th-seeded German Sabine Lisicki, who ousted the tall Russian in straight sets in a fourth-round Wimbledon match earlier this month.

Meanwhile, the former top-ranked Williams handled Canadian Aleksandra Wozniak 6-1, 6-3 on the famed Centre Court, where the American has captured no less than five Wimbledon titles.

"Every day I'm just concentrating on trying to bring my best tennis out," Williams said. "And honestly, if there's a time to do it, it's now."

Williams secured a singles gold medal at the 2000 Summer Games in Sydney.

The unseeded American should have her hands full with seventh-seeded German Angelique Kerber in the third round on Wednesday. The left-handed Kerber, who reached the Wimbledon semifinals earlier this month, whipped helpless Hungarian Timea Babos 6-1, 6-1 on Day 4 of this nine-day tournament.

Two other Germans joined Kerber in the round of 16, as the aforementioned Lisicki came from behind to beat Kazakhstan's Yaroslava Shvedova 4-6, 6-3, 7-5 and Julia Goerges grounded rising American Varvara Lepchenko 6-3, 7-5.

In addition to Sharapova, two more Russian seeds reached round three, as No. 14 Maria Kirilenko dismissed Brit Heather Watson 6-3, 6-2 and a No. 16 Petrova snuck past Georgian Anna Tatishvili 6-3, 6-7 (5-7), 6-2.

In some second-round doubles action on Tuesday, top-seeded Americans Liezel Huber and Lisa Raymond topped Polish sisters Agnieszka Radwanska and Urszula Radwanska 6-4, 7-6 (7-3) and the Williams sisters, Venus and Serena, erased a fifth-seeded tandem of Kerber and Lisicki 6-2, 7-5. The Williamses, now into the Olympic quarterfinals, captured the Wimbledon doubles title four weeks ago.

In some other third-round singles action on Wednesday, the fifth-seeded former No. 1 Serena will meet 13th-seeded Russian Vera Zvonareva; sixth-seeded Czech Petra Kvitova will take on Italian Flavia Pennetta; eighth-seeded former top- ranked star Caroline Wozniacki of Denmark will face Slovak Daniela Hantuchova; and 11th-seeded Serb Ana Ivanovic will tangle with fellow former No. 1 Kim Clijsters of Belgium.