Novak Djokovic of Serbia reacts during his ATP World Tour Finals first round tennis match against Nikolay Davydenko of Russia in London November 23, 2009. 
Serbia's Novak Djokovic, right, swaps shirts with Russia's Nikolay Davydenko, left, after their ATP World Tour Finals tennis match at the O2 Arena in London, Monday Nov. 23, 2009.
Czech Republic's Lukas Dlouhy, left, and India's Leander Paes, right, during their ATP World Tour Finals tennis match against Poland's Lukasz Kubot and Austria's Oliver Marach at the O2 Arena in London, Monday Nov. 23, 2009.
Robin Soderling of Sweden reacts after winning his ATP World Tour Finals first round tennis match against Rafael Nadal of Spain in London November 23, 2009.
Rafael Nadal of Spain reacts during his ATP World Tour Finals first round tennis match against Robin Soderling of Sweden in London November 23, 2009.
Novak Djokovic of Serbia reacts during his ATP World Tour Finals first round tennis match against Nikolay Davydenko of Russia in London November 23, 2009.
credit photo: AP