Katie Boulter lost for only the second time in her nine singles matches in the competitionKatie Boulter was unable to rise to the occasion like she has so often in the past as Great Britain went 1-0 behind in their opening Billie Jean King Cup Finals group tie against Kazakhstan.
British number three Boulter started well but opponent Yulia Putintseva fought back to win 4-6 6-3 6-2.
Harriet Dart, Britain's leading player in Emma Raducanu's absence, plays Wimbledon champion Elena Rybakina next.
Hosts Britain will lose the best-of-three tie in Glasgow if Dart is beaten.
If world number 98 Dart beats the Grand Slam winner, who is ranked 22nd, then the tie will be settled by the doubles match.
Doubles specialists Olivia Nicholls and Alicia Barnett have been picked by British captain Anne Keothavong and are set to make their debuts in the event. The doubles rubber is still played even if the tie has been settled as the result may yet have a bearing on the final group standings.
The Finals features 12 teams split across four groups, with the winners of the round-robin stage going through to the semi-finals.
Britain's uphill task made even harder
Britain did not qualify for the Finals after losing to the Czech Republic in April, instead being given a spot as the host nation when Glasgow was awarded the event.
Keothavong's team are ranked below Group C rivals Spain and Kazakhstan, leaving them with an uphill task made steeper by the absence of star player Raducanu.
The 2021 US Open champion was ruled out by a wrist injury, but the hosts hoped Boulter - who had won seven of her eight previous singles matches in the event - would help fill the void.
Boulter is a player who thrives on the big occasion, illustrated this year by her victory over former world number one Karolina Pliskova at Wimbledon, as well as her impressive record while representing Great Britain.
That looked to be a familiar plotline as she started confidently against Putintseva.
But the 26-year-old faded in the second set, and also needed treatment for what she described as a "tight" calf in the decider, as the Kazakh fought back to the delight of her nation's noisy traveling band of fans.
An aggressive start from Boulter, who broke twice for 2-1 without the Kazakh winning a point on her serve, proved key in the first set.
The second set turned in Putintseva's favour when she showed resilience and quality to win two long points on the way to breaking for a 4-2 lead.
After serving out to level, the world number 51 maintained the momentum and broke twice for 4-0 in the deciding set before confidently wrapping up a vital win.
