The 31-year-old, who has five Melbourne titles to her name, overcame Ayumi Morita 6-1 6-3 on Saturday.
Some wayward striking and a rare double-fault from Williams provided Morita with a pair of break points in game three, but the American found two big first serves to correct her errors and hold to 40.
Normal service was quickly resumed as the American broke to love in the following game before winning 13 of the next 18 points to seal the opening set inside 31 minutes.
Williams double-faulted again early in the second set and this time she was punished, as Morita broke to 15 before holding to 30 for a 3-0 lead.
However, that was as good as it got for Japanese player, who was overpowered in the next six games, in which she won just seven points.
The match, which lasted 66 minutes, saw Williams record the equal-fasted serve of her career - 207km/h.