Argentina won both singles rubbers on Friday to surge into a 2-0 lead in the semi-finals of the Davis Cup against Great Britain.
Home favourite Andy Murray led the charge for Team GB in front of his local crowd in Glasgow but failed to overcome the spirited Juan Martin del Potro.
Del Potro won silver behind Murray at the Rio Olympics and got revenge on his opponent, beating the Scot 6-4 5-7 6-7 6-3 6-4 to put Argentina 1-0 up after over five hours on court.
Delpo was understandably ecstatic after the match, praising the crowd and admitting that after so much injury heartache, he feels fortunate to be playing.
He told the BBC: "It was amazing for us. Thank you for the respect for both players. I really enjoyed the match. The crowd was great and the Argentinian fans great as well.
"I am so happy to be playing tennis again after three surgeries. This kind of moment was what I was missing at home and I always play good in Great Britain and here I played great so it is a good place for my tennis."
That left Kyle Edmund to try and level things for Great Britain against tricky left-hander Guido Pella.
Edmund started strongly, winning the first set in a tie-break, but could not capitalise as Pella took advantage to triumph 6-7 6-4 6-3 6-2 and give Argentina a 2-0 lead going in Saturday's doubles.
In the other semi-final, late call-up Richard Gasquet put France ahead against Croatia with a 6-2 7-6 6-1 win over Borna Coric but Marin Cilic hit back in Zadar with a 6-1 7-6 2-6 6-2 victory against Lucas Pouille.