The third decisive set was decided in a super tiebreak, which became dramatic.
Williams was 4-0 but Tan won five straight balls and then took home the match.
- I'm so full of emotions right now.
She's a superstar.
When I was a child, I watched her on TV so many times.
In my first Wimbledon - wow!
Wow just, says Tan.
Williams has been out of tennis for a year due to injury.
The 40-year-old is chasing his 24th grand slam title and is aiming for greater success at the US Open later this year.
- It was in the US Open that I won my first grand slam, it is super special.
I am clearly motivated to get better and play at home.
Williams has valleys far down the rankings, in 1204th place, and ifck a wildcard to the ongoing tournament.