Ons Jabeur, the No 2 seed, crashed out in the second round of the Australian Open after an error-strewn display in a 6-1, 5-7, 6-1 loss to the former French Open finalist Marketa Vondrousova on Thursday.
The Tunisian, who stormed up the rankings last year after runs to the final at Wimbledon and the US Open, sprayed 50 unforced errors and had her serve broken eight times in the 102-minute contest.
There were only flashes of the skills that have made her such a favourite on the WTA tour as Vondrousova matched everything Jabeur threw at her on a chilly evening on Rod Laver Arena.
Jabeur saved some face by breaking the Olympic silver medallist when she was serving for the match for the first time, but Vondrousova broke straight back to move on to a third-round meeting with her fellow Czech Linda Fruhvirtova.