Argentina was in sight of a first Davis Cup final since 2011 after taking a 2-0 lead over titleholder Britain thanks to singles wins by Juan Martin del Potro and Guido Pella in the semifinal.
Del Potro ended Andy Murray's 14-match winning streak in the Davis Cup, coming through 6-4, 5-7, 6-7 (5), 6-3, 6-4 in 5 hours, 7 minutes to gain a measure of revenge after losing the Olympic final to Murray last month. It was the longest match of both players' careers.
Pella beat Kyle Edmund 6-7 (5), 6-4, 6-3, 6-2, meaning the Argentines can clinch victory with a day to spare in Glasgow if they win the doubles on Saturday. Federico Delbonis and Leonardo Mayer are scheduled to play the Murray brothers, Andy and Jamie.
Whether Andy Murray plays is open to question.
"I'm very proud of how I fought, I did fantastic," Murray said. "I fought for every point, tried as best as I could. That's all you can do.
"It was very fine margins. That happens in tennis and sport sometimes. It could have gone either way." Del Potro gained the crucial break in the fifth set at the third opportunity, reaching Murray's angled volley with a forehand winner down the line to go 4-3 ahead, and he served out for the match, clinching victory with an ace and a big growl.