Azarenka on the march as Sharapova wobbles in Aussie Open
Belarus's Victoria Azarenka gestures during her match against Czech Republic's Barbora Zahlavova Strycova at the Australian Open tennis tournament in Melbourne on January 16, 2014 - by Mal Fairclough
The two-time title-holder crushed Czech Barbora Zahlavova Strycova 6-1, 6-4 in 88 minutes, benefiting from the roof being shut on centre court for her night match after another day of scorching heat.
There was no such luck for third seed Sharapova, the 2008 champion, who endured a brutal three-hour marathon against Karin Knapp in temperatures touching 42 Celsius (107.6 Fahrenheit) before the tournament's extreme heat policy was enforced.
"I can't complain about playing under the roof in the night session. It was a little bit humid. I mean, I still sweated a lot," said Azarenka. "But I can't complain."
"I felt I played pretty good," she added. "I'm glad that in important moments I'm finding my rhythm and I'm able to raise the level."
She next faces either Serbian 33rd seed Bojana Jovanovski or Austrian Yvonne Meusburger as she searches for a third consecutive Melbourne title, a feat last achieved by Martina Hingis between 1997-1999.
Sharapova is desperate to win a fifth Grand Slam, with her last coming at the French Open in 2012.
She had her work cut out with a third set lasting nearly two hours before downing Knapp 6-3, 4-6, 10-8 to set up a clash with France's Alize Cornet.
"I worked really hard in the last few months and I wanted this match," said Sharapova after making extensive use of ice vests and ice packs to keep cool in the sizzling conditions.
"I didn't play my best tennis; I didn't do many things well. But I got through it, and sometimes that's what's important."
It wasn't easy for the 26-year-old, who is coming back from a shoulder injury. Her serve let her down and she only converted seven of 20 break points against a gritty opponent who refused to give up.
Caroline Wozniacki, who this week said she had never been happier after getting engaged to golf star Rory McIlroy, also had a wobble against unseeded American Christina McHale.
The Dane, seeded 10, blasted through the first set 6-0 but her form then deserted her. She won just one game in the second before regrouping to take the third 6-3.
Like Azarenka, she benefited from the roof being shut.
"I was really, really pleased and happy about that," she said, expressing sympathy for Sharapova and Knapp having to brave the oven-like conditions.
Despite the wobbles, Wozniacki, who ended 2010 and 2011 as world number one but has never won a Grand Slam, said she believed she could finally make the breakthrough at Melbourne.
"I think you always believe you can win, but I still have quite a few matches to go. So I'm just thinking one match at a time," she said.
Another former world number one, Jelena Jankovic, seeded eight, also progressed, as did fifth seed Agnieszka Radwanska, a quarter-finalist here in all of the last three years.
Elsewhere, Young American Sloane Stephens, who made the semi-finals in 2013, came through a rain-interrupted three-setter while Spain's 16th seed Carla Suarez Navarro lived to fight another day.
Romanian 11th seed Simona Halep and 20th seed Dominika Cibulkova also survived on a day where play was halted for some four hours on the outside courts due to the heat.
World number one Serena Williams will be in action on Friday.