Roger Federer lost his first Davis Cup singles match in nine years as the United States took a surprise 2-0 lead over Switzerland.
World number 17 John Isner stunned Federer 4-6 6-3 7-6 (7-4) 6-2 in two hours and 40 minutes on clay in Fribourg, putting the Americans in the box seat in their World Group first round tie after Mardy Fish had earlier beaten Stanislas Wawrinka in a five-set marathon.
It looked like business as usual for Federer after claiming the first set in half an hour, but he failed to break Isner's serve again in the match as the American sent down 14 aces and 85 winners on his way to victory.
Earlier, Fish got the Americans off to the perfect start by beating Wawrinka 6-2 4-6 4-6 6-1 9-7 in a four hour epic, the last set alone lasting more than 90 minutes.
Spain began their title defence in perfect fashion, taking a 2-0 lead over Kazakhstan on clay in Oviedo.
In the absence of world number two Rafael Nadal, Juan Carlos Ferrero put Spain 1-0 as he defeated Mikhail Kukushkin 6-1 4-6 7-6 (7-2) 4-6 6-4, before Nicolas Almagro completed the clean sweep of the opening singles with a 6-3 4-6 6-1 6-1 victory over Andrey Golubev.
Last year's losing finalist Argentina also made a winning start to this year's campaign, taking a 2-0 lead over Germany in Bamberg.
Juan Monaco flourished on the German clay, beating Philipp Petzschner 6-3 6-3 6-3, before former Wimbledon finalist David Nalbandian recovered from a set down to defeat Florian Mayer 2-6 6-0 6-1 7-6 (7-5).
Japan and Croatia are locked at 1-1 after the first day in Hyogo, with Go Soeda rallying from two sets down to beat Ivan Dodig 6-7 (3-7) 3-6 6-4 6-3 7-5.
World number 20 Kei Nishikori could not build on his countryman's good work though, beaten 6-4 6-4 6-3 by Ivo Karlovic to leave the tie evenly poised.
Serbia look on their way to a comfortable victory over Sweden, with Janko Tipsarevic and Viktor Troicki losing just one set between them as they gave their nation a 2-0 lead.
World number seven Tomas Berdych beat Simone Bolelli in four sets as the Czech Republic took a 2-0 lead over Italy in Ostrava, while Juergen Melzer and Andreas Haider-Maurer both had wins as Austria jumped to a 2-0 lead over Russia.