Former world number one Victoria Azarenka lost her first match after a three-month injury layoff to Italy's Camila Giorgi at the ATP-WTA Eastbourne International on Tuesday.
The two-time Australian Open champion, who had not played since early March due to a foot injury, managed to stand the pace for nearly three hours before losing 4-6, 6-3, 7-5 to her 42nd-ranked opponent.
"I wanted a competitive match to test myself," said an upbeat Azarenka, 24, after the first round tie at the pre-Wimbledon grasscourt tournament.
"The most important thing was that I was there playing and I was healthy.
"I can always get better from here. I didn't expect a perfect match, but there are a lot of positive things that came out. I wanted to test myself and that's what I did.
"It feels great to know that I'm able to move how I want and not have my face like this (flinching) every time I step."
The Belarusian rallied from 4-2 down to win the first set but Giorgi, who has already beaten top ten players Dominika Cibulkova and Maria Sharapova this season, fought back.
The Italian, who played a first WTA final this year in Poland, came back in the second set and won despite nine double-faults after taking a 5-0 lead over Azarenka.
Giorgi, whose father-coach Sergio was going through every emotion in a dramatic display in the player box, levelled at a set each as world number eight Azarenka's early confidence appeared to fade.
The third set was tight until the seed gave away the sixth game for 2-4 with a double-fault, only to break back in the tenth to make it 5-5.
Azarenka was then broken for 5-6, with Giorgi serving out a game later as her opponent's return sailed long on match point.
The Italian next plays 109th-ranked British wild card Johanna Konta, who beat Swiss qualifier Belinda Bencic 6-3, 6-2.
"I had the desire, it was so important to see where I'm at and what I have to work on," said Azarenka, a semi-finalist in Wimbledon in 2011 and 2012.
"I need to work on timing, reaction and decision-making, things that you miss when you are away for a long time."
Second seed Petra Kvitova, a 2011 finalist, made a winning start over fellow Czech Lucie Safarova, 6-1, 5-7, 7-6 (7/4) advancing on a third match point.
American Madison Keys dealt third seed Jelena Jankovic a third career loss as the Serb fell 6-3, 6-3 and leaves without a victory at the venue.
Sixth seed Flavia Pennetta of Italy advanced into the second round at Devonshire Park over Hsieh Su-Wei of Taiwan 6-3, 6-3 while American Lauren Davis knocked out Italy's seventh seed Sara Errani 7-6 (7/5), 6-2.
Errani's doubles partner Roberta Vinci lost to Slovak Daniela Hantuchova 7-5, 6-1 while Varvara Lepchenko of the United States stopped China's Zhang Shuai 5-7, 6-4, 6-1.
In the men's draw, Finn Jarkko Nieminen began with an upset of seventh seed Santiago Giraldo, defeating the Colombian 6-3, 6-7 (5/7), 6-3 after suffering a leg problems last week in the Queen's third round.
A French pair advanced, with Julien Benneteau defeating Taiwan's Lu Yen-Hsun 6-2, 6-4 and Eduardo Roger-Vasselin beating Andrey Kuznetsov 6-3, 6-4.