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Both Williams and Osaka had withdrawn from warm-up events last week with shoulder issues but neither showed any sign of injury as they made swift progress to the second round, where they will also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.