Serbia is leading Belgium 3-0 with Argentina holding the same advantage over Germany as is France over Israel, but the rest are undecided going into the final day with Canada leading Spain 2-1, Italy over Croatia 2-1, the USA in front of Brazil 2-1, Kazakhstan beating Austria 2-1 and the Czech Republic in front of Switzerland 2-1.
After Djokovic's opening day singles win for Serbia over Olivier Rochus and his compatriot Viktor Troicki downing David Goffin, Belgium was on the ropes in Charleroi and then Serbia's doubles combination proved too good as well.
Troicki teamed with Nenad Zimonjic to beat Belgium pair Ruben Bemelmans and Steve Darcis 6-4, 6-4, 5-7, 6-4 to put Serbia through the quarter finals before the reverse singles.
France was already on top of Israel after opening day singles wins to top-10 pair Jo-Wilfried Tsonga and Richard Gasquet, and their doubles pair Julien Benneteau and Michael Llodra had little trouble with Jonathan Erlich and Dudi Sela, winning 7-6 (3), 6-1, 6-0 to put the French into the quarter finals.
The other country already through to the next round is Argentina with doubles pair David Nalbandian and Horacio Zeballos beating Germany's Christopher Kas and Tobias Kamke 6-1, 6-4, 5-7, 6-2 in Buenos Aires.
Meanwhile, Canada made an outstanding start against Spain on Friday making the most of the absence of Rafael Nadal, David Ferrero, Fernando Verdasco and Nicolas Almagro to win both singles matches.
However, Spain hit back in the doubles on Saturday with Marcel Granollers and Marc Lopez beating Daniel Nestor and Vasek Pospisil 4-6, 6-4, 6-7 (4), 6-3, 6-2 to force the tie into the reverse singles on Sunday.
Italy and Croatia were tied at one rubber apiece after singles wins to Andreas Seppi and Marin Cilic on Friday, and it was the Italians that took the 2-1 advantage on Saturday with Simone Bolelli and Fabio Fognini beating Cilic and Ivan Dodig 3-6, 6-1, 6-3, 7-6 (11).
United States pair John Isner and Sam Querrey had little trouble in their singles matches against Brazil on Friday, but the Brazilians hit back in the doubles with Marcelo Melo and Bruno Soares stunning record-breaking Americans Bob and Mike Bryan 7-6 (6), 6-7 (7), 6-4, 3-6, 6-3.
Kazakhstan was on top of Austria after winning both singles matches in Astana, but the Austrians hit back to take the doubles clash with Julian Knowle and Alexander Peya beating Andrey Golubev and Yuri Schukin 7-6 (5), 6-3, 7-6 (3).
Perhaps the tie of the opening round has been between the Czech Republic and Switzerland in Geneva.
The Czechs are the defending Davis Cup champions despite being without the hero of last year's final against Spain, Radek Stepanek but the Swiss are also missing Roger Federer.
Tomas Berdych and Stanislas Wawrinka won their singles matches on Friday to have the tie level at 1-1 going into the doubles, and it was an incredible seven-hour battle.
In the end, the Czech pair of Berdych and Lukas Rosol beat Wawrinka and Marco Chiudinelli 6-4, 5-7, 6-4, 6-7 (3), 24-22 with the epic surpassing the previous record in Davis Cup action when American John McEnroe beat Sweden's Mats Wilander in 6 hours and 22 minutes in 1982.
The previous longest doubles match took six hours and 20 minutes between Argentina's Nalbandian and Lucas Arnold, and Russia's Yevgeny Kafelnikov and Marat Safin in 2002.
The win gives the Czech Republic a 2-1 lead heading into the reverse singles that will see Berdych and Wawrinka have to back up against one another, with Rosol to also take on Henri Laaksonen.