Andy Murray was running on fumes as he as he kept Britain in the chase for a second straight Davis Cup final as he pulled the holders level 2-2 on Sunday.
The ironman Scot, who has logged more than 10 hours on court, was clearly struggling at the end as he beat Guido Pella 6-3, 6-2, 6-3 as the Argentine put a forehand into the net.
The Scot lost in opening singles to Juan Del Potro but teamed with his brother to give Britain the doubles point.
It now comes down to the deciding rubber - with mystery surrounding the possible non-participation of Argentina's Juan Del Potro, also out of gas after a gruelling weekend.
Dan Evans is expected to carry the hopes of the host nation into the final rubber.
"We were in a lot of trouble but now Dan has got the chance to go out there and get the job done," Murray told the BBC
"I had a lot of sharp pains in my quad, I'll just have to see what it is but my body needs a rest now. I've played so much tennis in the last few weeks.
"This makes a huge difference for all of us. We've had some great moments here in Glasgow and we need all your support for the next match."
In Zadar, Marin Cilic assured Croatia of only its second finals appearance in the worldwide team competition as the national number one thrashed Richard Gasquet of France 6-3, 6-2, 7-5, hammering 14 aces and producing 21 winners.
Croatia made its only other appearance in the title match in 2005, when Ivan Ljubicic - now coach of Roger Federer - led his nation past Slovakia in Bratislava.