With temperatures forecast to hit 39 degrees Celsius (102Fahrenheit), 2008 Australian Open victor Maria Sharapova hurried through the first set on Rod Laver Arena in 23 minutes before beating No. 14-seeded Anastasija Sevastova, 6-1, 7-6 (4).
"I think the surface of the court, I don't know how much heat, it's bad, very, very hot, and it's easy to get blisters and red", she said. No. 3-ranked Muguruza was the highest-ranked player to fall so far, but follows Venus Williams and U.S. Open champion Sloane Stephens out of the tournament in the first week.
Ninth-seeded Johanna Konta, the 2016 Australian Open semifinalist, fended off three match points before losing to US lucky loser Bernarda Pera 6-4, 7-5.
Taiwanese player Hsieh, 32 - who won 7-6 (7-1) 6-4 - will play 26th seed Agnieszka Radwanska in the third round. 'She's definitely a very tricky opponent, and even more if she plays well, ' Muguruza admitted.
"I look forward to these matches".
Roger Federer continued his career-long domination of Richard Gasquet, beating the Frenchman for the 17th time in 19 matches with a 6-2, 7-5, 6-4 third-round win at Melbourne Park.
Instead, she received only a warning from the match umpire. Apart from when she recovered from 5-2 in the first set and a brief rally at the end of the second, she was inferior against the former world doubles No. 1, whose box of tricks featured several shots not found in any tennis textbook.
The deficit was reduced, but when the pressure mounted and Hsieh served for the match, the former doubles world No.1 managed to strike a laser-like backhand passing shot, before closing out a career-best win in style with a smartly deflected backhand victor.More news: Haitians barred from applying for visas for low-skilled work in US
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A quarter-finalist in Melbourne previous year, the second-round defeat was Muguruza's earliest at the season's opening grand slam since she was beaten at the same stage in 2013.
She appeared to be going home after losing to Viktorija Golubic in the final round of qualifying but was given a place in the main draw following Margarita Gasparyan's withdrawal and has seized her second chance spectacularly.
Halep saved three match points in the 22nd game of the third set at 0-40 and Davis saved five break points in the 23rd game in the 3 hour, 45-minute match. "I want to be playing against opponents that have former Grand Slam champions", Sharapova said of a potential match against former No. 1-ranked Kerber.
Muguruza acknowledged that the heat was bothersome, but it wasn't the hottest conditions she'd experienced in Australia. I completely hate them.
Strycova beat Spaniard Lara Arruabarrena 6-3 6-4 in her second-round match. "I want to see where I am on that level". "I played one of my best games".
Karolina Pliskova, meanwhile, made light work of Beatrice Haddad Maia, winning 6-1 6-1 in just 44 minutes.