Novak Djokovic wins opening match in ATP World Tour Finals . The Serb will face Roger Federer on Sunday at the O2 Arena for a place in Sunday's final. Stanislas Wawrinka thrashes Tomas Berdcyh by same margin . It was the Serbian 's 11th straight victory at the end of season event and his 28th straight in matches played indoors . First day wins for Roger Federer and Kei Nishikori .
Novak Djokovic wins opening match in ATP World Tour Finals . The Serb will face Roger Federer on Sunday at the O2 Arena for a place in Sunday's final. Stanislas Wawrinka thrashes Tomas Berdcyh by same margin . First day wins for Roger Federer and Kei Nishikori .