Juan Martin del Potro defeated Andy Murry in an epic five-set encounter as defending champions Great Britain lost both of Friday's singles matches in their Davis Cup semi-final against Argentina.
Del Potro and Guido Pella gave the visitors a commanding lead in Glasgow as they saw off the challenge of Murray and Kyle Edmund respectively, to leave Britain facing an uphill task to retain their title.
Murray's 20-match winning streak at home in the competition was brought to a thrilling end after Del Potro edged a five-set thriller.
The Wimbledon champion's dominance on home soil for Great Britain had seen him win every rubber he had played, but he could not overcome a re-invigorated Del Potro.
The Argentine had to come back from 2-1 down in sets in the opening match, sealing his 6-4 5-7 6-7 (5-7) 6-3 6-4 win in five hours and seven minutes.
Since returning from his horrendous wrist injury Del Potro had beaten Novak Djokovic, Stan Wawrinka and Rafael Nadal, and he added Murray to the list with an accomplished display.
In a repeat of the Olympic Games final, which Murray won, Del Potro boomed down a plethora of forehands that caused his opponent no end of problems, and his big serve came to the fore at important moments - his 19th ace sealing victory.
Pella ensured victory in Saturdays' doubles will seal Argentina's place in the final after coming from a set down to beat Edmund 6-7 (5-7) 6-4 6-3 6-2.
The second semi-final between France and Croatia is evenly poised after the opening singles matches as Richard Gasquet and Marin Cilic started with wins.
Gasquet ran Borna Coric ragged in the first match in Zadar and cruised to a 6-2 7-6 (7-5) 6-1 victory.
A variety of ground strokes flew off Gasquet's racquet, with a number of inspired drop shots and crisp volleys to give the nine-time champions an early lead.
Coric's day was comprised by a niggling knee problem, the youngster let down by a string of unforced errors as he slipped to defeat.
Cilic ensured Croatia go into Saturday level with a 6-1 7-6 (7-4) 2-6 6-2 triumph over Lucas Pouille, the young Frenchman unable to summon the spirit that saw him beat Rafael Nadal at the US Open.
Victory for Cilic was his 13th in 16 Davis Cup singles rubbers and included 11 aces and 30 winners for the big-serving world number 11.