Juan Martin Del Potro won in his first match for nearly a year as he returned from a wrist injury that threatened his career.
The former world number four, 26, beat Ukraine's Sergiy Stakhovsky 6-3 7-6 (7-4) at the Sydney International ahead of the Australian Open.
Meanwhile, Agnieszka Radwanska, ranked sixth in the world, was knocked out by Garbine Muguruza 3-6 7-6 (7-4) 6-2.
Romanian Simona Halep has pulled out with a stomach bug.
The women's world number three's withdrawal follows that of Caroline Wozniacki, who suffered a wrist injury reaching the final of the Auckland Classic on Saturday.
Radwanska, 25, cited fatigue for her defeat. The Pole is now being trained legendary former player Martina Navratilova.
Argentine Del Potro, who won at the Sydney International last year before suffering his injury, said: "It's time to get back on the train."