(Reuters) - China's Li Na was forced into a dogfight in the heat before overcoming dogged American Christina McHale 7-6 7-5 to reach the second round of the Sydney International on Monday.

The former French Open champion, runner-up in Sydney last year and winner in 2011, took almost two hours to dispatch her the 33rd-ranked opponent in 30-degree temperatures.

China's Li Na hits a shot during her first round match against Christina McHale of the U.S. at the Sydney International tennis tournament January 7, 2013. REUTERS/David Gray

Fourth seed Li only arrived in Australia a day earlier, having beaten Klara Zakopalova to win the Shenzhen title, where the temperature outside hovered just above freezing.

"I was playing in China, so I have to (get) used to the heat," Li said of her decision to play Sydney and Shenzhen as she prepared for the Australian Open.

"I couldn't come straightaway to Melbourne. I needed some matches in the heat conditions, otherwise I don't know what I can do in Melbourne."

Adjusting to the heat on Monday, coupled with the long flight from China, the 2011 Australian Open runner-up said she had found the match against McHale mentally tough.

"Yes, very tough because in China it was like five, six degree, but here it's over 30," said the 30-year-old, who was playing an opponent 10 years younger.

"And the jet lag, time change, I was feeling today very tough. I (told) my team ... my legs (feel) like 200 kilos. I couldn't move.

"Yesterday the coach said (the most) important match is today, because today is really not for technique, it's challenging for your mind to show how strong you are on the court."

Li will face Ayumi Morita in the second round after the Japanese qualifier upset former top-10 player Daniela Hantuchova of Slovakia 1-6 6-3 6-3.

While Li struggled acclimatising, tournament organisers will be keeping an close eye on weather conditions on Tuesday.

Sydney is expected to hit a maximum of 43 Celsius as Australia swelters in a heatwave that has sparked raging bush fires.

Warm northwest winds are also expected to increase on-court temperatures closer to 50.

Officials will provide shading, ice towels and additional water and sports drinks for the players, while staff will work shorter shifts to try to mitigate the effects of the heat.

(Reporting by Greg Stutchbury in Wellington; Editing by Alastair Himmer)

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