SYDNEY — Former champion Li Na advanced to the second round of the Sydney International tennis tournament with a 7-6 (2), 7-5 win over Christina McHale on Monday. And Sam Stosur extended her miserable start to 2013 with another first-round loss.

The fourth-seeded Li, who won the Shenzhen Open last week, started her breakthrough 2011 season with a title in Sydney before reaching her first Grand Slam final at the Australian Open, then winning her first major at Roland Garros.

Top-seeded Agnieszka Radwanska of Poland extended her unbeaten start to the season to six matches with a 6-4, 6-3 win over 42-year-old Kimiko Date-Krumm early Tuesday.

Radwanska, who won last week’s WTA event in Auckland, New Zealand, secured an early break over the veteran Japanese player despite coping with searing temperatures that topped 100 degrees at Olympic Park.

“This is too hot to play tennis,” Radwanska said when shwe was asked whether matches should be put on hold at the warm-up event for the Australian Open.

“Even for players, for ball kids, for the people sitting out there, it’s just too hot.”

The ninth-ranked Stosur lost 6-3, 6-7 (7), 6-4 to Zheng Jie of China, her fifth loss in as many matches on Australian soil dating to last season.

The 2011 U.S. Open champion will head to the season’s first major at Melbourne Park next week with only two matches since minor ankle surgery six weeks ago.

In another upset result, American teenager Madison Keys defeated 17th-ranked Lucie Safarova of the Czech Republic 6-2, 6-1.

Former No. 1 Jelena Jankovic beat Tamira Paszek 6-2, 7-6 (5) to set up a showdown with unseeded Italian veteran Roberta Vinci, who upset eighth-seeded Nadia Petrova 7-5, 7-5.

French Open finalist Sara Errani advanced 6-1, 6-3 over Czech qualifier Karolina Pliskova and will go into a second-round match against Maria Kirilenko of Russia, a 7-5, 6-2 winner over Australian wild-card Olivia Rogowska.

In men’s matches, fifth-seeded Florian Mayer of Germany beat Joao Sousa of Portugal 6-1, 6-2; No. 8 Marcel Granollers of Spain had a 5-7, 7-5, 6-1 win over Matthew Ebden of Australia; and Denis Istomin of Uzbekistan defeated Australian qualifier James Duckworth 6-7 (4), 6-4, 7-6(3).

Australian Open

Djokovic, Azarenka top seeds: In Melbourne, Australia, defending champions Novak Djokovic and Victoria Azarenka will be the top-seeded players for the Australian Open.

Organizers stuck closely to the latest rankings to seed 32 players for each of the men’s and women’s draws.

The year’s first Grand Slam tournament starts next week.

Djokovic is followed by Roger Federer, U.S. Open champion Andy Murray and David Ferrer.

Ferrer replaces fellow Spaniard Rafael Nadal, who has withdrawn because a stomach ailment delayed his comeback from a knee injury.

On the women’s side, French Open champion Maria Sharapova is seeded second.

Serena Williams, the reigning Wimbledon, Olympic and U.S. Open champion, is seeded third.

Agnieszka Radwanska is seeded fourth, followed by Angelique Kerber and Li Na.

American teenager Sloane Stephens is seeded after advancing to a No. 29 ranking.

Heineken Open

Malisse, Rochus advance: In Auckland, New Zealand, Belgian veterans Olivier Rochus and Xavier Malisse beat higher-ranked opponents to advance to the second round of the Heineken Open.

American Brian Baker continued his surprising comeback by ousting fifth-seeded Jerzy Janowicz of Poland 4-6, 7-6 (5), 6-4.

The 89th-ranked Rochus, who reached the final in Auckland for the second time last year but needed a wild card to enter the main draw this time, beat 51st-ranked Albert Ramos of Spain 6-2, 5-7, 6-2. The 30-year-old Belgian’s victory improved his record in singles in Auckland to 14-7.

Rochus will play fourth-seeded Sam Querrey of the United States in the second round.

The top four seeded players in the Heineken Open — David Ferrer, Philipp Kohlschreiber, Tommy Haas and Querrey — received byes into the second round.

Earlier, the 32-year-old Malisse beat seventh-seeded Martin Klizan of Slovakia 7-6 (4), 3-6, 6-4. Malisse is rankedNo. 62. Also, eighth-seeded Thomasz Bellucci of Brazil defeated David Goffin of Belgium 7-6 (5), 6-2.

Hobart International

Hsieh, Schiavone out in first round: In Hobart, Australia. top-seeded Hsieh Su-wei lost to former doubles partner Peng Shuai of China 6-2, 6-7 (4), 7-6 (4) in the first round of the Hobart International.

Peng led 6-2 and 5-2 before her Taiwanese rival rallied to take the match into a third set. Peng took a 4-1 lead and wasted three match points before eventually overcoming the No. 25-ranked Hsieh.

Also, 2010 French Open champion Francesca Schiavone, seeded sixth, lost to Kirsten Flipkens of Belgium 2-6, 6-3, 7-6 (3).

Second-seeded Sorana Cirstea beat Nina Bratchikova 3-6, 7-5, 6-2 and No. 4 Yaroslava Shvedova beat Lourdes Dominguez Lino 6-4, 6-1.