INDIA, Nov. 12 -- World number one Rafael Nadal made a disappointing start at the ATP Finals as he suffered a first career loss to Germany's reigning champion Alexander Zverev, going down 6-2 6-4 on Monday.The Spaniard, seeking a first title at the event and hoping to secure the year-end number one ranking for a fifth time, showed no sign of the abdominal injury sustained in Paris this month, but was comprehensively outplayed.Djokovic will finish the year as world number one if he wins the tournament and Nadal does not reach the semi-finals.Alternatively, if the Spaniard fails to win a round-robin match, the Serb will overtake him if he wins two group-stage matches and reaches the final.Seventh seed Zverev has now beaten Roger Federer, Djok...