Serena Williams made her return to singles competition at Wimbledon after a four-year absence, but the 44-year-old American was defeated 6-3, 6-7(6), 6-3 by Australia's Maya Joint on Centre Court.
Williams, a 23-time Grand Slam champion, received a warm reception from the crowd. "It was really great to be back at Wimbledon," she said. "I definitely relished it and missed it and enjoyed the moment more than anything."
For the 20-year-old Joint, it was the biggest victory of her career. She will face 29th seed Alexandra Eala next.
In other notable results, defending champion Iga Swiatek survived a scare to win her first-round match. On the men's side, Stan Wawrinka, 41, played his final Wimbledon match, losing a lengthy five-set thriller to Matteo Berrettini.
American fourth seed Ben Shelton was the highest-ranked man to fall in the first round.