-LRB- CNN -RRB- -- World number two Novak Djokovic beat John Isner in a grueling four hour 16 minute encounter to secure Serbia 's passage into the quarterfinals of the Davis Cup on Sunday . Serbia led the United States 2-1 overnight in Belgrade with Djokovic favored to beat the giant Isner to clinch the tie , but he was given an almighty scare before winning 7-5 3-6 6-3 6-7 6-4 . They will now play Croatia at home on July 9-11 in the quarterfinals of the premier team event in tennis after their first-ever victory in the World Group . Djjokovic , urged on by a partisan home crowd , looked headed for a routine win as he took the opening set , but he was broken twice in the second as Isner leveled . Djokovic returned the compliment in the third set to lead two sets to one , but he could not force home the advantage and he lost a fourth set tiebreak 8-6 as Isner set up a decider . A single break in the first game gave Djokovic a crucial advantage , but his American opponent proceeded to save six match points before finally netting a forehand , the home hero sinking to his knees after an exhausting ordeal . The defeat means Patrick McEnroe 's U.S. team face a relegation playoff later this year to maintain their record of playing in the World Group every year . In other ties , defending champions Spain shrugged off the absence of the injured Rafael Nadal to beat Switzerland 4-1 to set-up a quarterfinal clash with France . Russia edged out India 3-2 and will face Argentina who defeated Sweden 3-2 in Stockholm . Returning from injury David Nalbandian was Argentina 's match winner in Stockholm as he beat Andreas Vinciguerra 7-5 6-3 4-6 6-4 in the deciding rubber after Swedish number one Robin Soderling had drawn them level with a straight sets win over Leonardo Mayer . 2005 champions Croatia , last year 's runners-up Czech Republic and France sealed their quarterfinal places on Saturday against Ecuador , Belgium and Germany respectively . France 's home clash with Spain is already whetting the appetite of tennis fans . `` It 'll be like a final , it 's the kind of thing you dream about , '' France captain Guy Forget told the official Davis Cup Web site www.daviscup.com .