Britain lost their opening ATP Cup tie after Jamie Murray and Joe Salisbury were beaten in a thrilling match in Sydney.
With the tie with Bulgaria locked at 1-1 after the singles, Salisbury and Murray lost 7-6 (7-5) 6-7 (2-7) 11-9 to Grigor Dimitrov and Alexandar Lazarov.
The Britons were unable to convert two match points in the match tie-break.
Britain started the inaugural event with Cameron Norrie’s win before Dan Evans lost to Dimitrov in the singles.
Norrie gave his side a 1-0 lead in the tie with a 6-2 3-6 6-2 victory over world number 423 Dimitar Kuzmanov, but Bulgaria levelled when US Open semi-finalist Dimitrov beat Evans 6-2 4-6 6-1 to set up the deciding doubles rubber.
That left Britain’s fate in the hands of Murray and Salisbury, playing together for the first time as the nation’s highest ranked doubles players.
But they were edged out in a tense finale to leave Britain, without the injured Andy Murray, needing to beat Belgium on Sunday to stand any chance of avoiding an early exit from the new 24-team tournament.
After the Bulgarian pair edged a tight first set, Murray and Salisbury broke early in the second set and maintained their slender advantage until the latter stages when Dimitrov and Lazarov swung momentum back in their favour.
Murray was unable to serve out the set at 5-4 as Bulgaria took their first break point since the third game of the match to level at 5-5.
Like the opener, it also needed a tie-break to separate the teams. But this time it was Britain who dominated, a beautiful lob by Salisbury teeing up four set points of which they needed just one when Dimitrov planted a volley wide.
That meant a first-to-10 match tie-break started about 2:30am at a sparsely-populated Ken Rosewall Arena, with Britain edging 4-2 ahead after a rare double fault from Dimitrov.
The mistake from former world number three Dimitrov did not prove costly, however, as the inspired Bulgarians fought back to 8-7 before showing more resilience to save the two match points.
Lazarov, ranked 477th in the doubles and outside the top 500 in the singles, put away a volley for 10-9 to tee up their first match point, which they took when he hit a perfect inside-out forehand down the line.
If it had not been for Andy Murray’s late decision to use his protected world ranking of two, Great Britain might not have qualified for the inaugural event because their other players may not have been ranked high enough.
But then the 32-year-old Scot, who only had career-saving hip surgery last January, announced on Saturday he would not play after “a setback” with the pelvic injury he has been nursing since the Davis Cup finals in November. James Ward was called up in his place.
Norrie, ranked 53rd in the world, was far from his best against the lower-ranked Kuzmanov, but eventually had enough quality to come through by converting his sixth break point of the match to win in almost two hours.
Murray’s absence means Evans, the world number 42, is Britain’s leading player and that pitted him against former world number three Dimitrov.
After a confident opening set where he broke serve three times, Evans lost his way in the second and allowed Dimitrov to level with a crucial break in what proved to be the final game of the set.
From that point Dimitrov took control and clinched victory in two hours and 16 minutes at about 12:10am local time, meaning the doubles rubber would not start until about 1am.