It was all about Marin in the second set, he stormed to win the last 5 games of the set, including a double break, and he was now 7-6 6-2 in front, needing just one more set to bring Croatia their second Davis Cup crown.
Croatia started in the final day with 2-1 lead, but Marin Cilic failed to beat Juan Martin del Potro of Argentina in a match that lasted four hours 53 minutes, losing the chance to secure the title. On Sunday was the turn of Federico Delbonis, who played out of his skin to settle the tie with a 6-3, 6-4, 6-2 victory over 6ft 11in Ivo Karlovic.
Argentina came from 1-2 down against Croatia to win the Davis Cup.
"This was an emotionally exhausting match and one of the biggest wins of my career", said Del Potro.
Saturday also saw the expected result, with Cilic and elite doubles player Ivan Dodig teaming to beat del Potro and Leonardo Mayer in a close but ultimately straight set doubles tie.
But much of the credit will go to Del Potro after the Olympic silver medallist, who missed the majority of 2014 and 2015 through injury, outlasted Cilic in an epic five-hour battle of former US Open champions. "Juan Martin won an incredible match and Federico played the match of his life".
Del Potro, the Comeback Player of the Year in the 2016 ATP World Tour Awards Presented by Moët & Chandon, joined Novak Djokovic, Andy Murray, Milos Raonic, Nick Kyrgios and Cilic as the only players with at least six Top 10 wins this year.
But Del Potro rebounded from his gold-medal defeat against Andy Murray in Rio and beat the three-time Grand Slam victor in five sets.
"Delpo showed his huge heart after turning around the match that looked lost", Orsanic told reporters after Sunday's victory.
Karlovic predictably claimed a hefty chunk of free points behind his big serve, but was punished for some sloppy play in the sixth game as Delbonis claimed the only break of the opener, before taking the set when his opponent sent a backhand return long.
Del Potro said he and Cilic are good friends on the tour, "but tomorrow will be a different situation".
"After losing the third set, I was still confident I could win as he looked exhausted", Cilic said.
He served out the match, sending the Argentine fans and their bench into jubilant celebrations.
The serving prowess of Karlovic got him out of a hole at 3-3 when, after he had failed to take a break-point opportunity of his own in the previous game, he fired down three aces in succession to recover from 15-40 down.