Williams received a wild card into the tournament 28 years after she first participated, making her the oldest player to date in the women's singles tournament.
However, the comeback on the big tennis stage was not a major success for the American.
Danilovic won 2–1 in sets (6–7, 6–3, 6–4) in the first round.
Williams' aging tennis arm was put to hard work in a match that lasted 2 hours and 19 minutes in the Melbourne evening heat. She held the upper hand for much of the match.
In the third set, Williams led 4–0 and looked to be on her way to victory. However, Danilovic fought back, tied the set at 4–4, and was able to turn the match around.
Williams made a comeback this summer after a 16-month hiatus and has only played sporadically on the tour in recent seasons. She is ranked 576th in the world.
She already has seven Grand Slam titles and four Olympic gold medals.
