Aryna Sabalenka’s first appearance since winning the Australian Open ended in defeat to Croatia’s Donna Vekic at the Dubai Tennis Championships.
Sabalenka lost 12 of the last 13 games as Croatia’s Vekic won 6-7 (5-7) 6-3 6-0 in their second-round match.
“The level was so bad from me,” said the Belarusian second seed.
World number one Iga Swiatek, who took the Doha title last week, won 6-4 6-4 against Sloane Stephens, while third seed Coco Gauff also progressed.
Gauff, who turns 20 next month, won 6-1 7-5 against Italy’s Elisabetta Cocciaretto, but it was far from straightforward to close out for the US Open champion.
With service games proving difficult for both players, Gauff was unable to see out victory at 5-4 but instantly broke back for 6-5 and ended a run of six successive breaks to take her second opportunity.
Gauff will face in-form Czech Karolina Pliskova in the last 16, while Swiatek meets Ukraine’s Elina Svitolina with the chance to avenge a defeat in the Wimbledon quarter-finals last year.
The top eight seeds received first-round byes in Dubai, meaning 2022 Wimbledon champion Elena Rybakina was among the host of WTA stars playing their opening match on Tuesday.
Rybakina, who won a title in Abu Dhabi before finishing runner-up to Swiatek in Doha, dropped the first set against Victoria Azarenka but won the second before the Belarusian had to quit through injury.
The Kazakh fourth seed plays Poland’s Magdalena Frech next, while Vekic’s reward is a meeting with Romania’s Sorana Cirstea.