Sofia Kenin's Australian Open title defence came to an end with a second-round loss to Kaia Kanepi on Thursday.
Kenin, who won her first and only grand slam title in Melbourne last year, fell to Kanepi 6-3 6-2 on a warm and windy day.
The American fourth seed had lost her only previous meeting against Kanepi and was again no match for the 35-year-old Estonian.
Kenin's second-round loss marked her earliest exit at a grand slam since Wimbledon in 2019.
She finished with 10 winners and 22 unforced errors, while Kanepi was far steadier with 22 and 17 respectively.
It continued a tough run for defending champions in Melbourne, where Victoria Azarenka was the last woman to go back-to-back in 2012 and 2013.
The last woman to defend any major crown was Serena Williams at Wimbledon in 2016.
Kanepi moved into the third round of a major for the first time since the 2019 French Open.
She will next face Croatian 28th seed Donna Vekic.