dWTA Grand Slam: if #1 oesn't win, the player who beat her also doesn't
However it sounds - it's the rule that *"started"* at 2021 Australian Open.
Iga Świątek won 2020 Roland Garros (postponed due to COVID-19, after US Open) beating Simona Halep who was #1 . This is actually the last Grand Slam tournament when #1 is beaten by later winner.
|Tournament|WTA #1 |Last match|Tournament winner| |:-|:-|:-|:-| |2021 Australian Open|Ashleigh Barty|QF (defeated by Karolína Muchová)|Naomi Osaka| |2021 French Open|Ashleigh Barty|Round 2 (retired during match vs Magda Linette)|Barbora Krejčíková| |2021 Wimbledon|Ashleigh Barty|Victory|\#1| |2021 US Open|Ashleigh Barty|Round 3 (defeated by Shelby Rogers)|Emma Raducanu| |2022 Australian Open|Ashleigh Barty|Victory|\#1| |2022 French Open|Iga Świątek|Victory|\#1| |2022 Wimbledon|Iga Świątek|Round 3 (defeated by Alizé Cornet)|Elena Rybakina| |2022 US Open|Iga Świątek|Victory|\#1| |2023 Australian Open|Iga Świątek|Round 4 (defeated by Elena Rybakina)|Aryna Sabalenka| |2023 French Open|Iga Świątek|Victory|\#1| |2023 Wimbledon|Iga Świątek|QF (defeated by Elina Svitolina)|Markéta Vondroušová| |2023 US Open|Iga Świątek|Round 4 (defeated by Jeļena Ostapenko)|Coco Gauff| |2024 Australian Open|Iga Świątek|Round 3 (defeated by Linda Nosková)|Aryna Sabalenka| |2024 French Open|Iga Świątek|Victory|\#1| |2024 Wimbledon|Iga Świątek|Round 3 (defeated by Yulia Putintseva)|Barbora Krejčíková| |2024 US Open|Iga Świątek|QF (defeated by Jessica Pegula)|Aryna Sabalenka| |2025 Australian Open|Aryna Sabalenka|?|?|