Great Britain began their inaugural ATP Cup campaign with a narrow 2-1 defeat against Bulgaria in Sydney on Friday.
Doubles pair Jamie Murray and Joe Salisbury needed to win their match against Grigor Dimitrov and Alexandar Lazarov to secure an overall victory.
But after the first two sets were shared following tiebreaks, it then came down to a final-set tiebreak which the Bulgarian pair took 11-9 in the early hours of the morning in Australia.
The tie had gone down to the final encounter after British number one Dan Evans surrendered a one-set lead to lose 2-6, 6-4, 6-1 to US Open semi-finalist Dimitrov in the second singles match.
Cameron Norrie had given his country the perfect start by overcoming Dimitar Kuzmanov, ranked 423rd in the world, 6-2, 3-6, 6-2.
The new 24-nation tournament features six groups of four teams. Each country plays three round-robin ties which are comprised of two singles matches and one doubles.
In the other Group C match, a Belgium team comprised of Steve Darcis, David Goffin and doubles pair Sander Gille and Joran Vliegen defeated Moldova 3-0.
Additional reporting by the Press Association.
