Williams started cautiously and showed signs of nervousness at the beginning of the first set, but then put in a higher gear and got to 13 serve.
- I am really happy with how I only fought for each point, Williams says in the victory interview after the match.
Williams, who has already won the US Open title six times, aims to break Australian Margaret Court's Grand Slam record with 24 victories.
Williams' Grand Slam title number 23 was at the 2017 Australian Open, when she was also pregnant with her daughter Olympia.
The last time the 38-year-old won the US Open was in 2014, when she did not lose a single set during the entire tournament.