Victoria Azarenka began her Australian Open title defence in stuttering fashion on Tuesday and Maria Sharapova was also made to fight, in contrast to Caroline Wozniacki who sizzled in the Melbourne heat.
Azarenka, the second seeded Belarusian, struggled in the opening set of her clash with world number 91 Johanna Larsson before finding some rhythm to progress.
It took her an hour and 46 minutes to get past the Swede 7-6 (7/2), 6-2 as temperatures soared towards 42 Celsius (107.6 Fahrenheit) in a game marred by unforced errors and poor serving.
"Sometimes it can be tricky, you know, to find your range, as it was today a little bit," she said, admitting she still needed to work on aspects of her game.
"I'll just try to keep the things that have been working before, what I was working on in Brisbane and my off-season and just try to reproduce it more and more and be disciplined with that."
The heat played a part in her lacklustre performance with Azarenka expecting the roof of the Rod Laver Arena to be closed as the temperatures rose.
"It's not easy. I thought they were going to close the roof for the second match, but, I mean, it's okay," she said.
"But I feel pretty good. Actually, I felt better as the match was going on than in the beginning."
Azarenka, who next plays unseeded Czech Barbora Zahlavova Strycova, is searching for her third consecutive Melbourne title, a feat last achieved by Martina Hingis between 1997-1999.
The woman she beat in the 2012 final, Sharapova, was also put through her paces by tough American Bethanie Mattek-Sands before clawing her way through 6-3, 6-4 in one hour and 39 mins.
"She was a tough opponent and I'm just happy to get through the first one," said the third seed, who is on the comeback trail from a shoulder injury that forced her off the tour in August.
Even at 11:00 pm, Sharapova was requesting an ice vest. Wozniacki also illustrated how hot it was by revealing that her water bottle started melting when she put it down on court.
Wozniacki dispatched Spain's Lourdes Dominguez Lino 6-0, 6-2 as she goes in hunt of a maiden Grand Slam title, with the final of the US Open in 2009 the deepest she has gone in a major so far.
The Dane, seeded 10, has struggled to revisit the highs of 2010 and 2011, when she finished both years as world number one.
But she is is determined to find more success, and said she was in a good place after getting engaged to golf star Rory McIlroy on New Year's Eve.
"I have achieved so much in my career already," she said. "But at the same time, when I go on court and when I play tournaments I want to win.
"For me right now I try to focus on the Grand Slams. It's tough, it's never easy. You have to win seven matches. There's always going to be some tricky opponents along the way.
"But that's what I'm missing on my resume, so that's obviously what I would like to achieve."
Fifth seed Agnieszka Radwanska, who has made the quarter-finals here for the past three years, needed three sets to stay alive but it was easier for 2008 semi-finalist Jelena Jankovic who went through in two.
Others safely into the second round included Spain's 16th seed Carla Suarez Navarro, French 25th seed Alize Cornet, courtesy of an early retirement, and Slovakia's Dominika Cibulkova.
Cibulkova beat veteran Italian Francesca Schiavone, who was playing her 54th consecutive Grand Slam. Only one woman in the Open era has bettered that total -- Japan's Ai Sugiyama, who played 62 in a row.