Unbeaten Britain took a giant step back to the top tier of Fed Cup competition with a gritty win over Bulgaria in the Red Sea city of Eilat.
Heather Watson won what turned out to be the deciding singles match 1-6, 6-4, 6-2 over Bulgaria's Tsvetana Pironkova after a breezy 6-0, 6-4 win for team-mate Laura Robson over Dia Evitmova in the opening match.
The result rounded out a perfect week for Team GB which included wins over Hungary, Portugal and Bosnia & Herzegovina.
Watson was assigned the tougher of the two singles matches on Sunday 10 February by Team GB coach Judy Murray, who was perhaps looking to challenge the world number 41 after a week of up-and-down performances in the Israeli city of Eliat.
Pironkova - one of the most underrated players in the women's game who has not only reached a Wimbledon semi-final but is also one of the few players to have beaten both Serena and Venus Williams in Grand Slam competition - took the first game 6-1.
Watson, however, fought back hard, breaking the 25-year-old late and holding on for a 6-4 win. Watson then broke Pironkova twice in the deciding game and took the match with a 6-2 win.
The victory puts Team GB through to the World Group II play-offs in April along with Poland, Kazakhstan and Canada
They'll be joined by the four nations which have lost their World Group II first round matches: France, Ukraine, Sweden and Belgium.
The times and locations of the ties will be announced on Wednesday 13 February.
Last year, the women narrowly missed out on the chance of promotion to the World Group after a 4-1 loss to Sweden in the World Group II play-offs in Boras, just outside Gothenburg.
This year's team is coached by Murray, mother of US Open champion Andy, and includes former British number one Anne Keothavong and Elena Baltacha.
Britain's Fed Cup team ended last season's competition ranked eighteenth out of the 94 nations participating. GB's best result in the 50-year-old tournament was a runner-up spot in 1981 - 12 years before Robson was born.