Serena Williams exits 2022 Wimbledon after losing in 1st round
Ranked 115th in the world, Tan, 24, won against 40-year-old Williams with sets of 7-5, 1-6, 7-6 (10-7) in a first-round match.
Tan will face Spain's Sara Sorribes Tormo in the women's second round.
Williams previously sealed the Wimbledon title in women's singles seven times, the last in 2016.
She suffered a leg injury in the 2021 Wimbledon which forced her to retire from the championships.
Williams returned to Wimbledon after a one-year absence due to the injury.
In the men's competition, Spanish star Rafael Nadal eliminated his Argentine opponent Francisco Cerundolo with sets of 6-4, 6-3, 3-6 and 6-4 to proceed to the second round.
Nadal, the world’s No. 2-ranked player, will play against Lithuania's Ricardas Berankis.
The 2022 Wimbledon, the third Grand Slam of the year, started Monday and will run through July 10.