Great Britain trail Slovakia 1-0 in their Fed Cup qualifier after Heather Watson was beaten in straight sets by Anna Karolina Schmiedlova.
Watson lost 6-2 6-3 to the world number 199 on clay at the AXA Arena in Bratislava.
The 27-year-old Briton, ranked 74, paid the price for only converting one of nine break points and 43 unforced errors.
Harriet Dart faces Viktoria Kuzmova in the second singles rubber on Friday.
The reverse singles and doubles rubber will be played on Saturday in the best-of-five tie.
The winner of the tie will join 11 other nations at the new Fed Cup Finals in Budapest from 14-19 April.
Watson lost the opening two games of the match, missing four break points in Schmiedlova's opening service game.
She fought back to 2-2 and was then 30-0 up on her serve but the Slovakian won the next four points at the start of a run of six consecutive games.
Watson steadied herself in the second set but was always trailing and was broken again in the final game, a forehand volley wide when faced with an open court all too typical of her performance.
Britain are without world number 14 Johanna Konta, who has opted to sit out the Fed Cup this year to protect her body, and Katie Boulter.
GB, who returned to the World Group for the first time since 1996 by beating Kazakhstan in a play-off last April, are among eight seeded nations in the qualifiers.
How does the new Fed Cup format work?
The eight winners of this week's qualifying ties will join 2019 finalists Australia and France, hosts Hungary and the Czech Republic in the new 12-team Fed Cup Finals, which will be played on clay in Budapest.
There is an $18m (£14.2m) prize fund and of that, $12m (£9.5m) will go to the players, and the other $6m (£4.75m) to their national associations.
The Laszlo Papp Budapest Sports Arena will host the finals until 2022 and there will be four groups of three teams, with the winners of each group progressing to the semi-finals.
Under the previous format, the champions needed to negotiate three home or away ties. Now they play no more than one.