MELBOURNE, Australia (AP)—Wimbledon champion Garbine Muguruza struggled with the heat in an upset second-round loss that left just three major winners in the Australian Open women's draw on Day 4.
Two of them will meet in the third round.
Maria Sharapova, the 2008 Australian Open winner, hurried through the first set on Rod Laver Arena in 23 minutes before beating No. 14-seeded Anastasija Sevastova 6-1, 7-6 (4).
Heat hovered around 40 Celsius (104 Fahrenheit) as 2016 champion Angelique Kerber set up a meeting with Sharapova with a 6-4, 6-1 win over Donna Vekic in a 70-minute afternoon match at Margaret Court Arena.
The crowd sang ''Happy Birthday'' and gave three hoorays to celebrate Kerber's 30th birthday. It was her 11th win, including the Sydney International title last week.
''Happy to be playing tennis again like 2016,'' said Kerber, who planned an ice bath before a relaxed dinner out in Melbourne to mark the occasion.
The heat intensified as six-time champion Novak Djokovic extended his personal streak against Gael Monfils to 15-0 with a 4-6, 6-3, 6-1, 6-3 victory in which both players slouched over in the shade at the back of the court between points.
The win was a relief for Djokovic, who says he's still not 100 percent after six months off the tour with an injured right elbow and who lost in a second-round shocker here last year.
Now seeded 14th, Djokovic needed four match points in an eight-minute last game before clinching the win against Mofils, who needed a medical time out for heat stress in the second set and said he had trouble breathing.
''It was obvious we both suffered on the court today,'' Djokovic said. ''Really tough conditions - brutal.''
It's supposed to be even hotter on Friday, with a forecast high of 42 Celsius (108 Fahrenheit).
Sharapova, who missed last year's Australian Open while serving a 15-month ban for a failed doping test, was happy to beat the player who'd ended her run at the U.S. Open last year.
''I did my job in two sets against someone that's been troubling in the past for me,'' Sharapova said. ''I think I deserve to smile out there after that victory.''
Muguruza had little to celebrate in a 7-6 (1), 6-4 loss to No. 88-ranked Hsieh Su-wei, who has been No. 1 in doubles but had only previously beaten one top 10 player in singles.
That left only Sharapova, Kerber and French Open champion Jelena Ostapenko as Grand Slam winners in the women's draw. Ostapenko plays her third-round match on Friday.
Muguruza acknowledged that the heat was bothersome, but it wasn't the hottest conditions she'd experienced in Australia.
''I could have done things better,'' she said, ''but at the end, she deserves to win.''
Considered one of the contenders for the title after Serena Williams opted against defending her Australian title, Muguruza had a troubled preparation including a retirement at the Brisbane International and a withdrawal ahead the quarterfinals in Sydney because of a right thigh injury.
Against Hsieh, she struggled with her serve, made 43 unforced errors. She needed a medical time out in the first set, and accidently hit a ball into a line judge in frustration.
Ninth-seeded Johanna Konta, the 2016 Australian Open semifinalist, lost in straight sets to U.S. lucky loser Bernarda Pera.
No. 123-ranked Pera is making her Grand Slam debut and, after losing in the last round of qualifying, didn't even know she had a spot in the main draw until Margarita Gasparyan withdrew.
''It feels amazing. I was ready to leave on Monday and then they told me I'm in, so I was obviously excited,'' Pera said. ''I was checking the tickets to fly back. I'm happy I didn't buy one.''
Pera will next play No. 20 Barbora Strycova.
U.S. Open finalist Madison Keys only needed 41 minutes for her 6-0, 6-1 win over No. 92-ranked Ekaterina Alexandrova, opening with four straight aces and winning the first 11 games.
Also advancing were No. 8 Caroline Garcia and No. 26 Agnieszka Radwanska, who next plays Hsieh.
Lauren Davis beat Andrea Petkovic 4-6, 6-0, 6-0 and has a potential third-round match against top-ranked Simona Halep, who had a later match against Eugenie Bouchard.
Former No. 1-ranked Karolina Pliskova advanced to a third-round match against No. 29 Lucie Safarova.
Men's seeds eliminated included No. 7 David Goffin and No. 13 Sam Querrey, who was beaten 6-4, 7-6 (6), 4-6, 6-2 by 80th-ranked Marton Fucsovics.
No. 5 Dominic Thiem rallied to beat 190th-ranked American qualifier Denis Kudla 6-7 (6), 3-6, 6-3, 6-2, 6-3 and No. 21 Albert Ramos beat another American, wild-card entry Tim Smyczek.
Also advancing were 2009 U.S. Open champion Juan Martin del Potro, No. 19 Tomas Berdych, No. 25 Fabio Fognini, No. 26 Adrian Mannarino and Chung Hyeon.