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 on Tuesday at the Sydney International.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 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."Radwanska said she was trying not to alter her game in the tough conditions, acknowledging that she had more of a battle against the heat than her opponent."The first main thing is just to stay calm and trying to survive," said the 2012 Wimbledon finalist, who said she has experienced similar conditions at Melbourne Park during the Australian Open.The Sydney tournament has an "Extreme Heat Policy" but it only comes into effect at the discretion of the tournament referee. Tennis officials apply a complex formula to such decisions, factoring in heat, humidity and wind to determine when on-court conditions become too stressful for players.In other women's matches, third-seeded Sara Errani of Italy and fourth-seeded Li Na of China easily advanced to the quarterfinals. Errani beat Russia's Maria Kirilenko 6-1, 6-1, while Li, who was pushed to two sets in beating American Christina McHale in the first round Monday, dominated Ayumi Morita of Japan 6-1, 6-0.Two-time Grand Slam champion Svetlana Kuznetsova, who had to qualify, beat former No. 1 Caroline Wozniacki 7-6 (4), 1-6, 6-2, while American qualifier Madison Keys defeated Zheng Jie of China 6-0, 6-4.In first-round men's play, sixth-seeded Radek Stepanek of Czech Republic defeated Guillermo Garcia-Lopez of Spain 6-2, 6-3, and Spain's Feliciano Lopez beat seventh-seeded Jeremy Chardy of France 6-7 (2), 7-5, 6-3.Jarkko Nieminen of Finland beat qualifier Bjorn Phau of Germany 6-0, 6-1, and Australian wild-card entry John Millman beat Spain's Tommy Robredo 6-3, 6-4.Top-seeded John Isner, who received a first-round bye, will play his second-round match against fellow American and qualifier Ryan Harrison. Harrison was leading Roberto Bautista Agut 2-1 in the opening set Tuesday when the Spaniard pulled out with a lower abdominal strain.