Updated

Defending champion Victoria Azarenka and five-time titlist Serena Williams easily advanced in their opening- round matches on Day 2 at the Australian Open.

The world No. 1 Azarenka handled Romanian Monica Niculescu by a 6-1, 6-4 score at Rod Laver Arena, while Williams overcame an ankle injury in the first set to rout Romania's Edina Gallovits-Hall on Tuesday.

"I started well but I struggled a little in the second set," Azarenka said after beating Niculescu.

Azarenka beat former champion Maria Sharapova in last year's Aussie Open final and lost to Williams in last year's U.S. Open title tilt. The Belarusian star's second-round opponent on Thursday will be Greek Eleni Daniilidou.

Seeking a third straight and 16th overall major title, the reigning U.S. Open and Wimbledon champion Williams, seeded third at this particular fortnight, rolled her right ankle less than 20 minutes into her opening-round match and then had to have her leg heavily taped. The injury had no bearing on the outcome, however, as she didn't lose a game in destroying Gallovits-Hall, 6-0, 6-0.

"I think I was really, really close to panicking because a very similar thing happened to me last year, almost on the same side, the same shot," Williams said. "I just had to really remain calm and think things through."

"Oh, I'll be out there," Williams said of her second-round match. "I'm alive. My heart's beating. I'll be fine."

The former No. 1 Williams' second-round opponent will be little-known Spaniard Garbine Muguruza.

Tuesday's play saw a couple of notable upsets, with seventh-seeded Sara Errani and Russian veteran Nadia Petrova both falling victim in their opening bouts.

Errani, the 2012 French Open runner-up and a quarterfinalist in Melbourne last year, was dealt a startling 6-4, 6-4 defeat at the hands of Spaniard Carla Suarez Navarro, while the 12th-seeded Petrova was ousted by 42-year-old Japanese Kimiko Date-Krumm, 6-2, 6-0.

Date-Krumm is now the oldest woman to win a singles match at Melbourne Park.

"Some players' mothers are younger than me," she laughed. "So it's like they're my daughter."

Former world No. 1 Caroline Wozniacki, who had lost in the first round of the last two Grand Slam events, survived her opener. The 10th-seeded Dane overcame a slow start to rally for a 2-6, 6-3, 6-3 victory over big-serving German Sabine Lisicki.

Up next for the former U.S. Open runner-up will be unheralded Croat Donna Vekic.

Former Wimbledon champ Petra Kvitova also had a tough time on Tuesday before prevailing, as the eighth-seeded Czech outlasted former French Open titlist and former Roland Garros runner-up Francesca Schiavone by a 6-4, 2-6, 6-2 count.

Kvitova could have her hands full with fellow lefty Laura Robson in the round of 64.

In some other top-20 action, 14th-seeded Russian Maria Kirilenko topped American Vania King 6-4, 6-2; No. 16 Italian Roberta Vinci handled Spaniard Silvia Soler-Espinosa 6-3, 7-5; No. 17 Czech Lucie Safarova got past Croat Mirjana Lucic-Baroni 7-6 (7-4), 6-4; and 20th-seeded Belgian Yanina Wickmayer dismissed Aussie Jarmila Gajdosova 6-1, 7-5.

Americans Varvara Lepchenko, Sloane Stephens and Jamie Hampton joined the parade into the second round. The 21st-seeded Lepchenko leveled Slovenian Polona Hercog 6-4, 6-1, while the rising 29th-seeded Stephens subdued Romanian Simona Halep 6-1, 6-1, and Hampton knocked out 31st-seeded Pole Urszula Radwanska 6-2, 6-4. Radwanska is the sister of last year's Wimbledon runner-up and world No. 4 star Agnieszka Radwanska. Stephens' second-round foe will be capable Frenchwoman Kristina Mladenovic.

One other seeded winner was No. 26 Su-Wei Hsieh of Taiwan, while some other seeded losers were No. 24 Russian Anastasia Pavlyuchenkova and No. 28 Yaroslava Shvedova of Kazakhstan.

Several other women reached the second round, including Russians Elena Vesnina and Svetlana Kuznetsova, the British Robson and Israeli veteran Shahar Peer. The two-time Grand Slam champion and former top-five star Kuznetsova clobbered Spaniard Lourdes Dominguez Lino 6-2, 6-1, while the promising Robson routed American Melanie Oudin 6-2, 6-3. Vesnina captured her first career WTA title in Hobart last week and will battle Lepchenko on Thursday.

The second round will get underway on Wednesday, with matches coming for the second-seeded French Open champion and former world No. 1 Sharapova, Radwanska and seven-time major champion and former top-ranked star Venus Williams. Sharapova will take on Japan's Misaki Doi, while the red-hot Radwanska, seeking her third title in three events so far this season, will encounter Romanian Irina-Camelia Begu, and a 25th-seeded Venus will face France's Alize Cornet. Venus lost to her younger sister Serena in the 2003 Aussie Open finale.

Also on the Day-3 schedule will be fifth-seeded German left-hander Angelique Kerber, sixth-seeded former French Open champion and former Aussie finalist Li Na, ninth-seeded former U.S. Open champion and heavy Aussie crowd favorite Sam Stosur, 13th-seeded former world No. 1 and former Aussie runner-up Ana Ivanovic, and 22nd-seeded former top-ranked star Jelena Jankovic.