Former Australian Open champion and world No.1 Angelique Kerber has saved two match points to set up a blockbuster second-round date with Venus Williams at the Sydney International.

Kerber overcame two rain delays and a tense second-set tiebreaker to eventually reign over crafty Czech Lucie Safarova 6-7 (3-7) 7-6 (10-8) 6-2 at Olympic Park on Monday.

The resurgent German’s victory extended her summer winning streak to five matches after an unbeaten singles run at the Hopman Cup and halted another day of carnage at the Open tune-up event.

Earlier, reigning US Open champion Sloane Stephens and eighth seed Anastasija Sevastova both lost their opening matches.

Italian qualifier Camila Giorgi swatted aside sixth-seeded Stephens 6-3 6-0 in 65 minutes to book a potential second-round showdown with dual Wimbledon champion Petra Kvitova.

Stephens’ swift exit in her first tournament of the year leaves the world No.13 alarmingly underdone heading into next week’s Australian Open in Melbourne.

But the 24-year-old is by no means the only big-name women’s player showing a lack of form entering the season-opening grand slam.

Sevastova is also on her way to Melbourne after falling 6-3 6-1 to former Open runner-up Dominika Cibulkova.

French Open champion Jelena Ostapenko, the world No.7, and the 11th-ranked Kristina Mladenovic also both bombed out in the first round on Sunday.

Australia’s big summer hope Ashleigh Barty posted her first win of the summer, grinding out a 6-3 6-4 victory over Paraguayan qualifier Veronica Cepede Royg to draw a line under last week’s first-round loss last week in Brisbane.

The world No.19 next faces Sydney wildcard Ellen Perez, ensuring at least one Australian in the quarter-finals.