Andy Murray fought through exhaustion, teaming with his brother Jamie to keep Britain alive 1-2 in the Davis Cup World Group semi-final against Argentina with a 6-2 3-6 6-4 6-4 doubles victory.
The must-win rubber for the holders in the worldwide team competition took nearly three hours, putting Andy Murray's court time over two weekend matches at eight hours.
"Yesterday was a very tough day and to get the win today with Jamie was great," Andy said. "He played unbelievably well throughout the whole match.
"Still 2-1 down is a tough position to be in but we're closer than we were at the beginning of the day and I still think we can come back." Captain Leon Smith added: "The Murrays have given us so many good moments as a team and we needed them. As soon as we heard Del Potro was coming in they showed their cards - they were trying to get the tie won today."
The effort comes after a season where the world No.2 won his second Wimbledon title and second gold at the Olympics before exiting early at the quarter-final stage of the US Open.
Murray will once again have to recover in time for what could be a key singles rubber on Sunday, final day of the indoor tie.
The Murray pair converted on five of 13 break points, with 44 winners and 23 unforced errors against the South Americans featuring Juan Del Potro and Leonardo Mayer.
Andy Murray sealed the tie on the first of three match points with an overhead winner at the feet of Del Potro.
Del Potro was competing in only his second Davis Cup doubles match after beating an Italian side in 2015. The loss to the Murrays ended an 11-match win streak in the competition for Mayer.
Britain won its first Davis title since 1936 last season, beating Belgium for the historic victory. Argentina are playing an 11th semi-final in the last 15 years.
The nations have met four times previously, with Argentina winning the last three meetings, most recently in 2008.
