Shanghai, China ? Confused and jittery after failing to win a game in the second set, Novak Djokovic rallied past Nikolay Davydenko, 7-6 (3), 0-6, 7-5, on Tuesday to reach the semifinals of the season-ending Masters Cup. Juan Martin del Potro of Argentina defeated Jo-Wilfried Tsonga of France, 7-6 (4), 7-6 (5).