Caroline Wozniacki’s first match on a grass court in five years ended in defeat by Elise Mertens at the Birmingham Classic.
Former world number one Wozniacki, who won the Australian Open in 2018, lost 6-4 6-1 to Belgian fifth seed Mertens.
Denmark’s Wozniacki, 33, returned to tennis last year, three and a half years after she retired at the 2020 Australian Open.
Britain’s Harriet Dart advanced to the second round with a 6-3 6-3 win over Japanese qualifier Moyuka Uchijima.
But Heather Watson suffered a 3-6 6-4 7-5 loss to eighth seed Marie Bouzkova in a tussle lasting two hours and 53 minutes.
Watson took a medical timeout after the second set and led 5-2 in the decider before Bouzkova hit back.
“I am super tired but I think it was a great match. What a way to start the grass-court season,” said Bouzkova.
British women’s number one Katie Boulter, who retained her Nottingham Open title on Sunday, is in action later on day two against Ukraine’s Anhelina Kalinina.
Compatriot Amelia Rajecki was beaten 7-5 6-3 by Russian Diana Shnaider in her first WTA main draw match.
