Sydney International: Angelique Kerber labours past Lucie Safarova, Sloane Stephens stunned by Camila Giorgi
Kerber will meet second-seeded Venus Williams who received a bye in the first round.
Sydney: Former No 1-ranked Angelique Kerber needed to save two match points before fending off Lucie Safarova 6-7 (3), 7-6 (8), 6-2 on Monday to set up a second-round match against Venus Williams.
Kerber, coming off a run to the Hopman Cup final in Perth, overcame two rain delays and a tricky second-set tiebreaker to extend her streak to five straight singles wins. Second-seeded Venus Williams had a bye in the first round.
The US Open champion Sloane Stephens lost her first match of the year, beaten 6-3, 6-0 by Italian qualifier Camila Giorgi and is short of match practice ahead of the Australian Open which starts in Melbourne next week.
World No 13 Stephens has not won a match since her breakthrough victory over Madison Keys in the US Open final.
The 24-year-old American took a two-month break from tennis after losing her last six matches in 2017 and is now on a seven-match losing streak.
Stephens' exit from Sydney came just one day after French Open champion Jelena Ostapenko was upset 7-6 (3), 6-1 by Ekaterina Makarova on the opening day of the Sydney tournament.
In other first-round matches on Monday, former Australian Open finalist Dominika Cibulkova beat No 8-seeded Anastasija Sevastova 6-3, 6-1 and Australia's Ash Barty posted her first win of the summer in a 6-3, 6-4 victory over qualifier Veronica Cepede Royg.
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Murray, who has finished runner-up in Melbourne on five separate occasions, is currently isolating at home, and is still hopeful of competing in the tournament.
A punishment would not be decided until after a full hearing. The ITF said Yastremska has a right to appeal, but has not yet done so.
Australian Open 2021: Tennys Sandgren allowed to board charter flight despite positive COVID-19 result
Sandgren was given a special clearance to board one of the flights from Los Angeles to Melbourne despite testing positive to COVID-19 in November and again on Monday.