MELBOURNE, Australia — Serena Williams cautiously walked onto the court, and tried to keep the points short to avoid irritating her injured right ankle as she advanced to the third round at the Australian Open.

Nineteen minutes later, she finished off a 6-2, 6-0 win Thursday over No. 112-ranked Garbine Muguruza with an ace at 128.7 mph — the fastest she can remember serving. “I’m on the up and up, I feel. It can only get better from here,” she said, adding that she wasn’t bothered by the ankle during the match.