MELBOURNE - Defending champion Victoria Azarenka breezed into the Australian Open third round Thursday in contrast to Maria Sharapova, who survived a big scare in sapping heat.

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.

Meanwhile, Title-contenders Rafael Nadal, Roger Federer and Andy Murray reached the Australian Open third round unscathed Thursday after extreme heat forced organisers to suspend play and close the stadium roofs. World number one Nadal, chasing his second Australian crown, overcame rising Australian teenager Thanasi Kokkinakis 6-2, 6-4, 6-2 under the closed roof on Rod Laver Arena. Nadal won match point not long after his great Grand Slam rival Federer wrapped up a 6-2, 6-1, 7-6 (7/4) win over Slovenia’s Blaz Kavcic on Hisense Arena. British fourth seed Andy Murray strung together an extraordinary winning sequence of 23 points to beat French qualifier Vincent Millot 6-2, 6-2, 7-5 in the night match on the main court.

Spanish top seed Nadal needed one hour and 53 minutes before extinguishing the 570th-ranked Kokkinakis in their first-ever meeting. Nadal broke the youngster’s serve five times and saved the three break points against him, but Kokkinakis acquitted himself well in the daunting task of playing the world number one before a full house. It was just the workout Nadal needed after playing just one set in his opening round when Australian Bernard Tomic retired injured.

“I think I played at a very good level. The serve, that is a very important thing here, was working well,” Nadal said.

“I played a great first set, not many mistakes, serving well, finishing the set playing aggressive with my forehand. Then I stopped a little bit in the second set and played with less intensity. “I finished the third set playing well again, good forehands down the line, like I did last year, so it’s the way to keep improving.”

Seventeen-time Grand Slam champion Federer, playing away from the main Rod Laver Arena court for the first time in 10 years, was in exquisite touch romping through the opening two sets in 54 minutes. The Swiss maestro blazed away for 52 winners, six service breaks and 11 aces to control his match with the 99th-ranked Slovenian. Kavcic could only shake his head and marvel at the brilliance of the four-time Australian Open champion, although he came more into the match in the final set when he forced a tiebreaker.

But Federer played the pressure points the better to finish well on top in front of an adoring Australian crowd. “It was a good first two sets. I played really aggressive and it worked out,” Federer said. “The third set he was more consistent. He served better. “In the process, it got closer. I’m happy I got it done in three.”

Murray, a three-time beaten finalist in Melbourne, was down two breaks in the final set against the 267th-ranked Millot, but reeled off the last 23 points to get a double break and serve out for the match. Former finalist Jo-Wilfried Tsonga also profited from the heat-prompted switch to indoor conditions to breeze past Brazilian Thomaz Bellucci 7-6 (8/6), 6-4, 6-4 and into the last 32. Japan’s Kei Nishikori mastered Dusan Lajovic to advance to the third round in straight sets.

The Japanese 16th seed kept the match to just one hour 49 minutes before prevailing 6-1, 6-1, 7-6 (7/3) over the Serb. Nishikori, now coached by former French Open champion Michael Chang, reached the third round for the fourth consecutive year. American Donald Young upset Italian 24th seed Andreas Seppi in five sets, and Spain’s 31st seed Fernando Verdasco was knocked out by Russian Teymuraz Gabashvili in another five-setter.

There was an even bigger upset when former US Open champion Juan Martin del Potro, the fifth seed, was sent crashing by Spain’s 62nd-ranked Roberto Bautista Agut. But France’s Benoit Paire saw off a stiff challenge from Australian teenager Nick Kyrgios to go through in five sets. Elsewhere, power-serving Canadian Milos Raonic blasted 27 aces in ousting Romania’s Victor Hanescu in straight sets.