Andy Murray battled for more than four hours but was beaten over five sets by Roberto Bautista Agut in the first round of the Australian Open in what could be his final professional match.
Of the seven British players in action, only Katie Boulter and Dan Evans were victorious, with last year's semi-finalist Kyle Edmund losing in straight sets to Tomas Berdych.
Evans will now face Roger Federer, who eased into round two along with Rafael Nadal, Caroline Wozniacki and Angelique Kerber.
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Forty winks
Rafael Nadal covered a range of serious topics in his press conference including the Majorca floods and ATP politics but was reduced to schoolboy giggles when he noticed well-known Italian journalist Ubaldo Scanagatta had nodded off. "It's not interesting today," he said with a raised eyebrow.
Land of the giants
It is not often that John Isner has to look up when he shakes hands at the net but that was the case when he took on fellow American Reilly Opelka in the tallest grand slam match on record.
The 21-year-old, who is officially listed at 6ft 11in, one inch taller than Isner, made his advantage count to win a match that was inevitably settled by tie-breaks, Opelka winning 7-6 (4) 7-6 (4) 6-7 (4) 7-6 (5). The pair hit 87 aces between them.
Fallen seeds
Women: Julia Goerges (14), Jelena Ostapenko (22), Barbora Strycova (32)
Men: John Isner (9), Kyle Edmund (13), Steve Johnson (31)
Who's up next?
Serena Williams returns to grand slam action for the first time since her row with umpire Carlos Ramos overshadowed the US Open final.
The 16th seed takes on fellow mother Tatjana Maria while the player who beat her – fourth seed Naomi Osaka – is also in action on Rod Laver Arena against Magda Linette.
Johanna Konta is the sole British player on court and faces Ajla Tomljanovic, while Simona Halep, Novak Djokovic and Alexander Zverev also begin their campaigns and Milos Raonic plays Nick Kyrgios in a much-anticipated night match.