London, Nov 4 (EFE).- Spain's Rafael Nadal must win at least two matches at the Barclays ATP World Tour Finals, which started at London's O2 Arena on Monday, to remain at No. 1 and deny Serbia's Novak Djokovic the top spot in the ATP rankings.
The 27-year-old Spanish star is hoping to win the season-ending tournament for the first time.
Nadal, who is playing in his sixth year-end tournament, will play his first match on Tuesday against countryman David Ferrer and will later play the other members of his group, the Czech Republic's Tomas Berdych and Switzerland's Stanislas Wawrinka.
The Spanish star will lock up the No. 1 ranking if he wins two of his three group matches in London; otherwise, he will have to wait and see how Djokovic performs at the season-ending tournament and in the Davis Cup final pitting Serbia against the Czech Republic, an event that starts on Nov. 15 and could give "Nole" a maximum of 225 points.
If Nadal wins just one match, the Serbian will have to go undefeated in winning the event in London and earn points from two victories in Davis Cup action to grab the No. 1 ranking.
Djokovic could grab the No. 1 spot if he wins the Masters Cup and Nadal does not win any matches in London, and he could lose up to one match on the road to victory in the British capital in this scenario.
Nadal will open play against Ferrer, while Djokovic is scheduled to play Switzerland's Roger Federer in a later match on Tuesday.
The Spanish star, who wrested the No. 1 ranking away from Djokovic last month, has had an extremely successful season, winning his eighth French Open title and second U.S. Open crown.