World number five Juan Martin del Potro and Wimbledon semi-finalist Jerzy Janowicz will join defending champion Bernard Tomic at the Sydney International in January, organisers said on Sunday.
Argentina's Del Potro, 25, has enjoyed a strong year with titles in Basel, Tokyo, Washington and Rotterdam and featured in this month's ATP World Tour Finals in London.
"I know the fans like when I hit my forehand really strong. I like to share moments with the crowd and in Sydney the fans create a great atmosphere for the players," Del Potro said.
Rising Polish star Janowicz, ranked 21, will play the Sydney event for the first time in the run-up to the Australian Open in Melbourne, the year's opening Grand Slam.
Australia's Tomic, ranked 51, will be defending his maiden ATP title.
"Winning Sydney really changed me and made me feel that I can win these tournaments. I'm really looking forward to coming back and having a shot at defending my title," Tomic said.
Polish world number five Agnieszka Radwanska will defend her women's title in Sydney from January 5 to 11.