Heather Watson was unable to clinch victory for Great Britain at the first time of asking in their Billie Jean King Cup play-off tie against Mexico.
With Britain leading 2-0 overnight, Watson knew beating Marcela Zacarias would give the hosts an unassailable lead in the best-of-five tie.
However, the world number 68 lost 6-3 7-6 (7-1) in London to an opponent ranked 138 places below her.
Katie Boulter can seal victory against Giuliana Olmos later on Saturday.
If Boulter also loses, the tie will go to a deciding doubles match.
The second singles match will take place at 16:15 BST, with the day’s play at the National Tennis Centre paused to mark the funeral of Prince Philip.
The Billie Jean King Cup is the new name for the Fed Cup, the women’s international team event that Britain have finished runners-up in four times but have never won.
If Anne Keothavong’s team manage to secure victory against Mexico they will progress to the 2022 qualifiers, where another win will put them in next year’s eight-team finals.