Bernard Tomic defeated top-ranked Novak Djokovic 6-4, 6-4 to give Australia a 1-0 lead over Serbia at the Hopman Cup on Wednesday.
Tomic put pressure on Djokovic from the opening game, holding five break points, and faced just one break point against him.
Teenager Ashleigh Barty will attempt to seal victory for Australia when she faces Ana Ivanovic.