Serena Williams began her pursuit of a record-equalling 24th Grand Slam singles title with a dominant 7-5 6-3 win over fellow American Kristie Ahn.
The 38-year-old went a break down in both sets but gathered momentum, winning four straight games against the world number 96 in the second set.
“I was really happy with how I fought for every point,” she said.
“No matter how I was playing, I just had to get my Serena focus back so that was what I was working on today.”
However, she will not be joined in the next round by her sister Venus Williams, who lost 6-3 7-5 to Czech 20th seed Karolina Muchova.
An error-strewn performance meant that two-time champion Venus, 40, made her first-ever opening-round exit at her home Grand Slam.
Meanwhile, women’s 10th seed Garbine Muguruza sealed her place in the second round with a 6-4 6-4 win against Japan’s Nao Hibino.
Seventh seed Madison Keys is through after beating Hungary’s Timea Babos 6-1 6-1, while American second seed Sofia Kenin claimed a 6-2 6-2 victory against Belgium’s Yanina Wickmayer.