Kim Clijsters saw her latest WTA Tour comeback ended by Hsieh Su-wei at the Chicago Fall Tennis Classic on Monday.
The four-time grand slam champion, playing in her first match of 2021, was defeated 6-3 5-7 6-3 in a contest lasting two hours and 18 minutes on Stadium Court.
Clijsters, who retired in 2012, made her return to the Tour last year, losing her three matches.
After knee surgery at the end of 2020 and having contracted COVID-19 this year, the 38-year-old at last made her first appearance of the season but was bested in a gruelling contest by Australian Open quarter-finalist Hsieh.
Speaking prior to her return in Chicago, Clijsters spoke of how she was drawing inspiration from Andy Murray, who continues on the ATP circuit despite two major hip surgeries.
"Seeing Andy Murray and the way he speaks about his comeback and everything, it's so motivating and it gives you a lot of energy too," she said. "To see him go through the things he's gone through and be open about the challenges of it and the belief that he has, I feel like it's something I can relate to."
Seeds Jessia Pagula, Danielle Collins and Veronika Kudermetova all progressed in Chicago on Monday, although home favourite Madison Keys had to retire from her match with Aliaksandra Sasnovich.