Great Britain's Davis Cup defence is hanging by a thread after Juan Martin del Potro beat Andy Murray to set Argentina on their way to a 2-0 lead on day one of the semi-final in Glasgow.
Del Potro won 6-4 5-7 6-7 (5-7) 6-3 6-4 after five hours and seven minutes, before Guido Pella saw off Kyle Edmund 6-7 (5-7) 6-4 6-3 6-2.
Murray's defeat was only his third in 32 Davis Cup singles matches.
GB must win Saturday's doubles and both Sunday's singles to reach the final.
Murray is scheduled to team up with his brother Jamie for the doubles contest but admitted it would be "really tough" for him to recover following the longest match of his career on Friday.