The World Group was the highest level of Davis Cup competition in 2013. The first-round losers go into the Davis Cup World Group Play-offs, and the winners progress to the quarterfinals. The quarterfinalists were guaranteed a World Group spot for 2014. Czech Republic defended their Davis Cup title, by defeating the Serbian team in Belgrade in the final.
Switzerland vs. Czech Republic
The doubles match was the second longest match of all time (7 hours and 1 minute).
References
2013 Davis Cup World Group Wikipedia(Text) CC BY-SA