Borna Coric kept his cool to prevail in a thrilling winner-takes-all duel with fellow young gun Frances Tiafoe on Sunday and steer Croatia into the final of the Davis Cup for the second time in three years with a monumental 3-2 victory over the US
The 21-year-old Coric came from two sets to one down to defeat the 20-year-old debutant Tiafoe 6-7(0), 6-1, 6-7(11), 6-1, 6-3 and finally subdue a remarkable fightback from the Americans, who had earlier levelled the tie 2-2 from two down.
Late understudy Sam Querrey had rewarded captain Jim Courier's gamble by taking the tie into a decider in the fourth rubber, battling back from the brink of two sets down to beat home talisman Marin Cilic 6-7(2), 7-6(6), 6-3, 6-4.
Yet with everything resting on the first duel between two of tennis's brightest young 'Next Gen' men, Coric overcame the loss of two very contrasting tiebreaks to book Croatia's final date against champions France.
The French, who defeated Spain 3-2 in the other semi-final in Lille, will have home advantage in the November showdown and hope to avenge their 3-2 loss to the Croatians in the 2016 semi-final.
For a moment, though, after Coric had capitulated 7-0 in the first set breaker and 13-11 in the third set decider, the shocked fans in the Dalmatian resort feared Croatia could be on the wrong end of one of the competition's unlikeliest comebacks.
Coric, though, demonstrated why he is seen as one of the sport's best prospects, holding his nerve against the brilliant young American and proving to be too solid over the final two sets as he finally prevailed after four hours six minutes.
At 2-0 down after Friday's singles, there had not seemed the remotest chance of a U.S. team without their top two players John Isner and Jack Sock recovering to reach a first final in 11 years.
Only when 40-year-old Mike Bryan and Ryan Harrison fought courageously to claw out a five-set doubles win on Saturday, were the Americans given even faint hope.
But Courier was rewarded for a bold, if slightly desperate-looking risk when he rested his No.1 Steve Johnson and instead threw Querrey into the must-win fourth rubber even though the 30-year-old had never previously beaten Cilic in six attempts.
Cilic had also become the most successful Croatian Davis Cup player in history on Friday when winning his 37th rubber against Tiafoe but the world number six was found wanting when, after winning the opening set on a tiebreak, he stood on the verge of a commanding lead.
He took a 6-1 lead in the second set tiebreak in superb fashion only to crumble under Querrey's onslaught with the American world number 61 winning seven straight points.
"I just hung in there. After being 6-1 down in the tiebreak, I just played aggressively and from then on the pressure just builds," said Querrey.
Cilic's early dominance on the outdoor clay, cheered by an enthusiastic crowd in the Dalmatian resort, then evaporated as Querrey took the next two sets to win in three hours and eight minutes.