Bulgaria's best female tennis player Tsvetana Pironkova. Photo by EPA/BGNES
Great Britain secured a Fed Cup World Group II play-off in April after winning their Euro/Africa Group I play-off against Bulgaria in Eilat, Israel, BBC reported.
Laura Robson put them ahead with a 6-0 6-4 victory over Dia Evtimova.
British number one Heather Watson lost the first set in 25 minutes against Tsvetana Pironkova but captured five successive games to win 1-6 6-4 6-2.
On Wednesday, Britain will learn who they face in the Group II play-off on 20-21 April.
World number 45 Robson was quickly in command against Evtimova, ranked 253, taking the first set in 21 minutes.
Evtimova briefly threatened by breaking the Robson serve early in the second set, but the British number two swiftly broke back and finished things off neatly in under an hour, her fifth win out of five this week.
Watson lost seven games in a row against world number 44 Pironkova but secured her first break of the match in the seventh game of set two and soon took charge of the deciding set, surging into a 4-0 advantage.
Pironkova, 25, broke the Watson serve to get back to 4-2, but Watson promptly broke back then held serve to wrap up Britain's victory.