Cameron Norrie ensured Great Britain started the inaugural ATP Cup with a victory after battling past Bulgaria's Dimitar Kuzmanov in three sets.
British number two Norrie, ranked 53rd, won 6-2 3-6 6-2 against the world number 423 in Sydney.
Dan Evans takes on US Open semi-finalist Grigor Dimitrov in the second singles match later on Friday.
Jamie Murray and Joe Salisbury then play the doubles rubber in the best-of-three tie.
After taking on Bulgaria, Britain face Belgium on 5 January and Moldova on 7 January in their other round-robin ties.
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 alongside British number one Evans and Norrie as the singles players, with doubles specialists Jamie Murray and Salisbury completing the five-man team.
The 24-nation event features six groups of four teams, who each play three round-robin ties. The ties - comprising two singles matches and one doubles - are best of three.
The six group winners, plus the best two runners-up, will progress to the quarter-finals.