Kim Clijsters produced a remarkable display in her first WTA match in nearly eight years, which ended in a 6-2 7-6 (8-6) defeat by Australian Open finalist Garbine Muguruza in Dubai.
The Belgian, 36, went toe-to-toe with Muguruza from the baseline, produced several stunning winners and came from a double-break down in the second set.
But Muguruza finally saw off Clijsters with a big serve in the tie-break.
This is the Belgian's second comeback, having first retired in 2007.
Back then, injuries and the intention to marry and have a child resulted in the 2005 US Open champion stepping away from the sport.
Clijsters made a successful return to tennis in 2009, adding two more titles at Flushing Meadows and an Australian Open crown in 2011 before announcing her plan to quit the sport again in 2012.
The Belgian, who now has three children, announced in September 2019 her decision to make a second comeback.
As a former world number one, Clijsters is eligible for unlimited wildcards at WTA tournaments, and she can choose the number of events she wishes to compete in - which she said was a major factor in her decision.
Muguruza praises Clijsters display
Clijsters, who has also won three Tour finals, lacked sharpness in the first set before going 3-0 down at the start of the next.
But she then began to find the sweet spots with her groundstrokes as Muguruza struggled with her own serve.
The Spaniard recovered her form and took the set to a tie-break, which was decided by a huge first serve.
The Belgian said: "I had a good feeling out there, I felt a pace I can handle. I felt like I was able to go toe-to-toe with her from the baseline.
"I have patience. I'm going to work my way into it and fight. We'll see what happens."
Former Wimbledon champion Muguruza added: "A player that can play incredible can play incredible again."