Davis Cup holders Great Britain completed the first step of what would be an amazing comeback as they beat Argentina in Saturday's doubles.
Andy and Jamie Murray kept defending champions Great Britain alive in the Davis Cup semi-finals with a doubles victory over Juan Martin del Potro and Leonardo Mayer.
The British team found themselves 2-0 behind after the singles matches on Friday with Argentina recording victories through Del Potro and Guido Pella.
That placed huge pressure on the doubles rubber and the Murray brothers duly delivered, the 6-1 3-6 6-4 6-4 win halving the deficit with two singles matches to come on Sunday.
Great Britain will still need to win both if they are to successfully defend their title, but Andy Murray will take confidence and hope that Del Potro tires in a potential decider with Kyle Edmund.
Croatia have the advantage in the second semi-final thanks to Marin Cilic and Ivan Dodig, the duo beating France's Pierre-Hugues Herbert and Nicolas Mahut 7-6 (8-6) 5-7 7-6 (8-6) 6-3 in Zadar.
Cilic and Dodig turned on the style in the fourth set to take a 2-1 lead, the latter particularly impressive with a clinical, focused performance.
Victory leaves them one rubber away from the final, with Cilic hoping to seal the point they require when he meets Richard Gasquet on Sunday.
Meanwhile, four countries secured their place in the 2017 World Group with 3-0 victories. Japan, Australia, Spain and Belgium comfortably dispatched Ukraine, Slovakia, India and Brazil respectively.
Olympic gold medallists Marc Lopez and Rafael Nadal - back after a bout of gastroenteritis - secured Spain's return to the top level, the pair seeing off Leander Paes and Saketh Myneni in four sets.