The 28-year old from Tandil, whose injury woes started in 2010, staged an astonishing comeback from two sets down to beat Croatia's Marin Cilic 6-7(4) 2-6 7-5 6-4 6-3 and haul Argentina back on to level pegging in the final against the Balkan nation.
Roared on by several thousand frenetic away fans in the Zagreb Arena, Federico Delbonis then blew away Ivo Karlovic in straight sets in the decisive rubber.
But all the glory went to Del Potro, who revealed after the match with Cilic that he had played through the fifth set with a broken finger and that he came close to hanging up his racket during a lengthy spell on the sidelines.
"My finger is broken but I won't mind one bit if we win the Davis Cup," he told a news conference while keeping an eye on a big screen as Delbonis was in the middle of dismantling Karlovic.
"It happened in the fifth set when I tried to catch a serve from Cilic which was out.
"This was an emotionally exhausting match and one of the biggest wins of my career. Thanks to all those who prevented me from retiring; I was very close to never playing again and, well, here I am."
Cilic made the brighter start against his close friend and on-court nemesis, who has now won nine of their 11 meetings in all competitions, including the last six.
Looking weary and moving around with some difficulty, Del Potro looked out for the count after Cilic clinched the first set tie-break and then raced through the second set.
