Sydney - Former world No 1 Angelique Kerber won her sixth consecutive match of the new season, beating second-seeded Venus Williams 5-7, 6-3, 6-1 on Tuesday in a Sydney International match delayed for two hours by a thunderstorm.
Kerber, who dropped to No 22 following a poor 2017 season, needed to save two match points before beating Lucie Safarova in three sets on Monday.
She won four consecutive singles matches at the Hopman Cup last week.
Williams was playing her first match in Sydney since winning the gold medal at the 2000 Olympics.
"I say goodbye to 2017 and I'm really happy that the new year's beginning," Kerber said.
Former champion Agnieszka Radwanska ended Johanna Konta's defense with a 6-3, 7-5 win. The fourth-seeded Konta was playing her first match since retiring from her Brisbane International quarter-final last week with a hip injury.
The Sydney-born Konta said she had no pain during her near two-hour match.
"Actually, it was good," Konta said. "So that was a really positive thing for me today, that it held up fine and I recovered well from that."
Former US Open champion Samantha Stosur won her first-round match, beating Carina Witthoeft 4-6, 7-5, 6-3.
In men's first-round play, Australian teenager Alex De Minaur followed up his semi-final appearance at the Brisbane International last week, including a second-round upset win over 2016 champion Milos Raonic, with a 6-4, 6-2 victory over Fernando Verdasco.
Leonardo Mayer had a 7-5, 6-3 upset win over eighth-seeded Mischa Zverev.