Former world number one and two-time Grand Slam winner Garbine Muguruza announced her retirement from tennis on Saturday after more than a year without playing.

Women's 26th seed Elise Mertens was another winner, with the Belgian outlasting Spain's Garbine Muguruza, who was seen cramping before losing 3-6, 7-6 (7/3), 6-1.

Bianca Andreescu staged a dramatic comeback Sunday to topple Garbine Muguruza in a battle of former Grand Slam champions on day one of the Adelaide International

Top seed Djokovic brushed aside 79th-ranked Thanasi Kokkinakis of Australia 6-1, 6-4, 6-2 and will face Serbian compatriot Miomir Kecmanovic for a last-16 place

Wimbledon: Garbine Muguruza, 2017 Champion, Loses To Greet Minnen In Rd 1

Alize Cornet sent Garbine Muguruza crashing out of the Australian Open in the second round Thursday, upsetting the Spaniard 6-3, 6-3.

Australian Open: Muguruza carried that form on to Rod Laver Arena against 77th-ranked Frenchwoman Clara Burel, proving too powerful in winning 6-3, 6-4 in 88 minutes

World number three Garbine Muguruza said Saturday that the "real truth" about what happened to Peng Shuai may never be known after the tennis star accused a senior Chinese politician of sexual assault.

Muguruza will now play another Russian, Daria Kasatkina, in the quarter-finals after she upset Belgian Elise Mertens 6-3, 6-4.

Nick Kyrgios and former world number one Andy Murray will play in the Sydney Tennis Classic, which begins on January 10, ahead of the Australian Open.