Champions Russia were given a real fright before Davis Cup debutant Nikolay Davydenko managed to squeeze his country into the quarter-finals by winning the deciding singles against the Czech Republic on Sunday.
World number 52 Ivan Ljubicic turned the formbook on its head single-handedly to give Croatia a 3-1 winning lead over the mighty United States.
With France, Spain, Australia and Argentina having already booked their last-eight places on Saturday, they were joined by Switzerland and seven-times champions Sweden.
After tasting Davis Cup success for the first time last December, it seemed Russia's celebrations would be short-lived as they looked in danger of succumbing to the artistry of the Czechs.
The under-strength Russians, missing the injured Marat Safin and with Yevgeny Kafelnikov clearly below his best, had to rely on the 21-year-old Davydenko to carve out a 1-6, 7-6, 6-2, 3-6, 6-0 win over Radek Stepanek and gain the 3-2 margin.
Kafelnikov, omitted from the original singles line-up, failed to capitalise on his late call-up for the ailing Mikhail Youzhny in the first match of the day.
An out-of-sorts Kafelnikov appeared to put in little effort during the opening two sets and fell 6-2, 6-3, 7-6 to Jiri Novak, which levelled the tie at 2-2.
But Davydenko did not let the occasion get to him and boldly went for his shots to set up a meeting with Argentina in the next round.
The United States, champions a record 31 times, were left to lick their wounds when they fell at the first hurdle for the second time in three years.
With Andre Agassi, Pete Sampras and Andy Roddick all missing from the U.S. team, the inexperienced duo of James Blake and Mardy Fish could do little to stop the Croatian charge.
Ljubicic put in an inspirational display and made the home fans in Zagreb delirious after handing Croatia an unexpected 3-1 winning lead following a 6-3, 6-7, 6-4, 6-3 victory over the 24th ranked Blake in the first reverse singles.
Ljubicic, who had also won his opening singles before teaming up with Goran Ivanisevic to triumph in the doubles on Saturday, used his huge serve to come from a service break down in the third set to claim a famous victory.
"This is big for me, especially because I won all three matches," an elated Ljubicic said.
"When you are number one, your team mates expect you to win at least two matches, maybe three, so it's a lot of pressure. But I didn't feel one bit of nerves yesterday or today."
The result put Croatia into the last eight for only the second time in their history.
LITTLE TROUBLE
Their quarter-final opponents Spain had little trouble in completing a 5-0 whitewash of Belgium in Seville.
Juan Carlos Ferrero beat Kristof Vliegen 6-1, 6-4 and Carlos Moya thumped Christophe Rochus 6-2, 6-2.
Switzerland and Sweden were stretched to the limit before they scraped tense 3-2 victories over the Netherlands and Brazil respectively.
Swiss Michel Kratochvil beat Dutchman Martin Verkerk 1-6, 7-6, 7-6, 6-1 in a nail-biting deciding rubber to set up a last-eight clash with France, 4-1 winners over Romania, in April.
Trailing 2-1 after Saturday's doubles match, Switzerland's Roger Federer levelled the tie earlier in the day when he outclassed Sjeng Schalken 7-6, 6-4, 7-5 in the first reverse singles.
Sweden also had to win both of their reverse singles against Brazil on Sunday before securing a meeting in the next round with Australia.
Jonas Bjorkman edged out Gustavo Kuerten 6-4, 6-4, 4-6, 4-6, 6-1 while Andreas Vinciguerra had an easier time in sweeping past Flavio Saretta 6-1, 7-5, 6-3.
A depleted Germany team, without the services of Tommy Haas, failed to negotiate their first-round opponents for the second year running and suffered an embarrassing 5-0 defeat to Argentina in Buenos Aires.
