Watson is in second place on the list for most singles matches won by a British player in the Fed Cup/Billie Jean King Cup with 23Great Britain will have to fight back from behind to reach the Billie Jean King Cup final after Heather Watson lost the opening rubber of the semi-final against Australia in Glasgow.
Watson, 30, lost 6-4 7-6 (7-3) to Storm Sanders as Britain try to reach the final for the first time since 1981.
If Harriet Dart loses to Ajla Tomljanovic in the next singles rubber, Australia will secure victory.
If the Briton wins, the best-of-three tie will go to a deciding doubles.
Great Britain had played their previous two ties in the evening and the change to a morning start on Saturday seemed to affect Watson.
"I think I just didn't feel as fresh as I did then," she said. "It's very different playing at 10am when we have been having late starts.
"[But] I really enjoyed being out there on court today again."
Great Britain have been the underdogs throughout the competition and face another uphill task to reach the final after Watson's defeat.
But one thing we have learned about Anne Keothavong's side this week is not to write them off.
Having initially failed to qualify for the event, they were handed a spot as the host nation and put into a difficult group with Spain and Kazakhstan, who are both ranked higher than the Britons.
They had also suffered another a blow before the 12-team finals started when Emma Raducanu - the 2021 US Open champion and Britain's highest-ranked player - was ruled out through injury.
After losing to Kazakhstan on Tuesday, they could have been eliminated before even playing Spain on Thursday.
But Spain, led by former world number two Paula Badosa, won 3-0 against Kazakhstan in their opening group match, meaning Great Britain then needed to beat them 3-0 - which they did in a stunning performance that Keothavong described as "something really special".
Watson was brilliant in Thursday's must-win group tie against five-time champions Spain as the hosts reached the last four, but could not reach the same level against an opponent ranked 104 places below her.
Sanders is better than her current ranking of 237 suggests, illustrated by her recent form on the ITF Tour and she has taken that into the BJK Cup Finals this week.
Starting confidently and aggressively, the 28-year-old dominated Watson from the early exchanges and that led to a break for 2-1 in the opening set from which Watson could not recover.
The British number six, backed by noisy support from the biggest crowd of the week, broke for 2-0 in the second set but could not hold on to the lead as Sanders recovered to earn her fifth win of the week.
"I don't feel like I played as well as I did in the first match [against Spain], I felt a bit heavier today, missed a lot more first serves," said Watson, who won only 57% of her first serves.
