Third-seeded Angelique Kerber secured the first spot in the quarterfinals of the Brisbane International with a 6-3, 7-5 win over Daria Gavrilova on Tuesday.
Varvara Lepchenko also advanced with a 6-4, 6-4 win over fellow American Madison Keys, who had ousted Australian Open finalist Dominika Cibulkova in the first round.
In a men's first-round upset, Lukasz Kubot of Poland beat fifth-seeded Kevin Anderson of South Africa 7-6 (3), 6-4.
At the ASB Classic in Auckland, New Zealand, Venus Williams made short work of her first match of the new year by sweeping past Slovakia's Jana Cepelova 6-4, 6-0 in 52 minutes.
Williams, seeded third behind Caroline Wozniacki and Sara Errani, appeared fit and served 10 aces.
The seven-time major winner reached the final of the Auckland hard-court tournament last year.