MELBOURNE, Australia (AP) -- Just the thought of playing in the sweltering heat at the Australian Open is keeping Serena Williams up at night.
So to combat the soaring temperatures, the 17-time Grand Slam champion is doing her best to stay indoors, rolling through her matches as quick as possible.
On Wednesday, the American beat No. 104-ranked Vesna Dolonc 6-1, 6-2 and equaled an Open era record held by tennis great Margaret Court with her 60th match win at the Australian Open.
''I kept waking up in the middle of the night last night, just paranoid,'' Williams, who regularly trains in the Florida heat, said after dropping only three games for the second straight match.
''I just wanted to stay hydrated,'' Williams said. ''The last thing I want to do is to cramp in this weather. It can happen so easy.''
If the forecast of four consecutive days of 40-plus degrees Celsius (104-plus degrees Fahrenheit) temperatures in Melbourne proves correct, it will be the worst heat wave in the city in more than a century.
After two days of temperatures touching 42 degrees C (108 degrees F), the forecast is for 44 C (111 F) on Thursday.
That will make conditions brutal again for the likes of Maria Sharapova, who opens play on the center court on Day 4 of the season's first major, and top-ranked Rafael Nadal, who has a late afternoon match.
After peaking at 2 p.m. Wednesday, the temperature dropped significantly later in the afternoon, and Australian Open tournament referee Wayne McKewen for the second consecutive day said the low humidity made it unnecessary to invoke the Extreme Heat Policy.
Overhead clouds and the lack of a hot breeze made it less stifling than the previous day.
A Grand Slam record-equaling nine players retired during the first round, when some were describing the conditions for playing matches as dangerous and inhumane.
No. 32 Ivan Dodig joined the list on Wednesday, retiring with cramps in the fourth set against Bosnian qualifier Damir Dzumhur. Dodig created a stir when he was reported as saying he thought he could die.
But tournament doctor Tim Wood again said it wasn't hot enough to endanger professional players.
''There were only a couple of court calls today related to the heat and no player required medical intervention,'' he said.
Williams concedes there is a stage in the heat when the body goes into auto-pilot, regardless of the preparation.
''Sometimes my body just says no to hot weather,'' she said. ''Sometimes I have no reaction.''
Three-time defending champion Novak Djokovic has struggled in the Australian heat before, but has conditioned himself to deal with it. Even so, he was happy to get off the court in less than two hours with a 6-0, 6-4, 6-4 win over Leonardo Mayer - his 26th in a row since September.
Also advancing were No. 3 David Ferrer, No. 7 Tomas Berdych, No. 8 Stanislas Wawrinka, No. 9 Richard Gasquet and Sam Querrey, the highest-ranked American still in the men's draw, who upset No. 23 Ernests Gulbis.
Those progressing on the women's side included two-time finalist Li Na and No. 9 Angelique Kerber. Two Aussies advanced - 2011 U.S. Open champion Samantha Stosur and wild-card entry Casey Dellacqua, who upset No. 18 Kirsten Flipkens 6-3, 6-0.
That side of the draw plays again Friday. Williams will meet Daniela Hantuchova, who has won more matches in three sets than any active player on the women's tour. The No. 31-seeded Hantuchova spent 3 hours, 13 minutes out on the exposed Court 13 in her 6-3, 3-6, 12-10 win over Karolina Pliskova.
Williams has won eight of their nine previous encounters, with Hantuchova's sole victory coming in the third round at the Australian Open eight years ago.
The 30-year-old Slovakian revels in the heat, and the long matches, and cited it as a factor in her only win over Williams
''I made her move,'' Hantuchova said, ''and suffer in the heat.''