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Serena Williams launched her latest bid for a record-equalling 24th Grand Slam with a 56-minute demolition of Laura Siegemund at the Australian Open.
US Open champion Naomi Osaka also made a convincing start with a 6-1 6-2 win over Russia's Anastasia Pavlyuchenkova.
But former champion Angelique Kerber was the first seed to be knocked out.
The German 23rd seed, who was one of 72 players to spend 14 days in 'hard' quarantine before the tournament - confined to a hotel room and unable to train outside - was beaten 6-0 6-4 by American Bernarda Pera.
Both Williams and Osaka had withdrawn from warm-up events last week with shoulder issues but neither showed any sign of injury as they made swift progress to the second round, where they will also be joined by Williams' 40-year-old sister Venus, who beat Belgium's Kirsten Flipkens 7-5 6-2.
Osaka will play France's Caroline Garcia next, while the elder Williams sister faces veteran Sara Errani.
French Open champion Iga Swiatek raced into the second round with a 6-1 6-3 win over Arantxa Rus of the Netherlands, but US Open quarter-finalist Tsvetana Pironkova of Bulgaria lost 7-5 6-2 to Taiwanese Hsieh Su-wei.
Hseih will next play Canada's Bianca Andreescu, who beat Mihaela Buzarnescu 6-2 4-6 6-3 in her first match for 15 months.
The 2019 US Open champion had not played for 467 days after struggling with a knee injury.
"I've been through quite a bit in those 15 months. It wasn't easy," she said.
Williams made a nervy start against Siegemund, double-faulting on the first point of the match before losing her opening service game.
However the American, who withdrew from last week's Yarra Valley Classic semi-final with a shoulder problem, did not take long to find her footing.
She hit 16 winners and four aces against 51st-ranked Siegemund, setting up a second-round meeting with Serbia's Nina Stojanovic.