MELBOURNE (AFP) - World No. 5 Venus Williams and US Open champion Sloane Stephens were high-profile casualties on day one of tennis' Australian Open on Monday, but Roland Garros winner Jelena Ostapenko survived.
Men's top seed Rafael Nadal, meanwhile, ruthlessly brushed aside Victor Estrella Burgos to power into the second round.
Williams, who lost in the final to sister Serena last year, was stunned by Swiss star Belinda Bencic, fresh from winning the Hopman Cup with Roger Federer.
The seven-time Grand Slam winner, in her 77th grand slam event, struggled against a player who had never before beaten her to go down 6-3, 7-5 and deprive the tournament of one of its biggest names.
It is the first time since 1997 that there will be neither of the Williams sisters in the second round, with Serena not playing after giving birth to her first child.
"I would like to have played someone easier," said Bencic. "When I was a little girl watching on TV I would never imagine I would play them (the Williamses)."
World No. 1 Nadal, beaten in the final by his great rival Roger Federer last year, clinically took apart the 81st-ranked Dominican to forge a 6-1, 6-1, 6-1 win in 94 minutes on Rod Laver Arena. He next plays Leonardo Mayer of Argentina.
"I'm very happy to be back, it's a very important beginning for me. It's good news for me," he said.
Like Venus, also out of the opening Grand Slam of the year is American big-hitter CoCo Vandeweghe, a semi-finalist last year at Melbourne Park and Flushing Meadow. She slumped out to Hungary's Timea Babos 7-6 (7-4), 6-2.
Vandeweghe was given two code violations during her stormy defeat at the Hisense Arena.
The first came after she refused to restart play at the end of the first set until a ball-kid delivered her bananas.
"How are they not on court? I mean, c'mon, that's not my fault," she said during an argument with the chair umpire.
The American was then docked a point towards the end of the second set after appearing to curse at 51st-ranked Babos.
Stephens' poor run since winning at Flushing Meadows in September continued, with the 13th seed crashing out to Chinese No. 2 Zhang Shuai, who made the last eight two years ago.
The frustrated American put in an error-strewn performance on an overcast and windy Melbourne day and has now not won in seven matches.
"I'm not going to get too down," said Stephens after her 2-6, 7-6 (7-2), 6-2 defeat. "I'm just going to stay positive and keep working to get back in the best shape and best place possible to do well for my next tournaments."
There was better luck for Ostapenko, who saw off Francesca Schiavone 6-1, 6-4. The seventh seed raced through the first set on Rod Laver Arena against the veteran Italian who was bizarrely wearing a back brace on the outside of her shirt.
She was 4-1 down in the second before knuckling down to race home and a second round clash with China's Duan Yingying.
"I knew before the match that it's not going to be easy. She's very experienced player and she's very long time on tour," said the Latvian. "I knew I had to play really aggressive and stay very consistent."
Also into the next round with a straight-sets win was German 12th seed Julia Goerges, who won the lead-up Auckland Classic and is now on a 15-match unbeaten streak having ended 2017 with victories at Moscow and Zhuhai.
World No. 2 Caroline Wozniacki, who lost to Goerges in that New Zealand decider, kept her quest for a first Grand Slam title on course, cruising into the second round in straight sets.
The second-seeded Dane overcame tricky Romanian Mihaela Buzarnescu 6-2, 6-3 on the Margaret Court Arena in an hour and 11 minutes.
"I knew it as going to be tough and I had to try to fight for every point," said Wozniacki, who played an almost flawless match with just five unforced errors to her opponent's 33.
I knew she would be a dangerous floater."
Australia's big hope, the volatile Nick Kyrgios, toyed with opponent Rogerio Dutra Silva to storm into the second round, collecting a code violation along the way.
The 17th seed was on autopilot throughout as he disposed of the 100th-ranked Brazilian 6-1, 6-2, 6-4 in 87 minutes. He played a flawless opening set but that did not stop him from receiving a code violation early in the match.
Kyrgios was serving for a 4-1 lead when he told a member of the crowd to keep quiet during his service motion in colourful language that did not go down well with chair umpire.
Before his match, Nadal, the 16-time Grand Slam champion, insisted that he was feeling fine despite struggling with a knee injury and ready to go deep at an event that he has only won once - in 2009 - among his string of major triumphs.
This is despite a chequered lead-up that prevented him playing a warm-up tournament for the first time ever ahead of the event.
"It's a new situation for me. But I feel good," said the 31-year-old, who first played at Melbourne Park in 2004.
Fellow multiple Grand Slam winner Novak Djokovic, seeded 14th, starts on Tuesday, along with former world No. 1 Maria Sharapova and top seed Simona Halep.
Among men safely through to the next round are 31st seed Pablo Cuevas and Ukrainian Alexandr Dolgopolov.