Andy Murray is within striking distance of the No. 1 ranking, and he could supplant Novak Djokovic in the next two weeks due to a technicality.
Murray (10,485) is currently 2,415 points behind Djokovic (12,900), and he can only add a maximum of 1,500 points during that period—500 for winning this week's ATP event in Vienna, and 1,000 points for winning next week’s BNP Paribas Masters in Paris.
If the Scot wins those two tournaments, he’ll still be 915 points behind Djokovic, with 1,500 points still on offer at the ATP Tour Finals. But Murray could take the top spot before then because points from the ATP Tour Finals, unlike other events, drop off a week before the tournament is played.
Murray (9,685) is only 915 points behind Djokovic (10,600) for the season, and could move in front of the Serb with good showings in Vienna and Paris. If he does pass him, the ATP has indicated, that Murray will become the top-ranked player during the week between the Paris Masters and the ATP Tour Finals.
As the defending champion in London, with two round-robin victories at the Tour Finals, Djokovic could drop 1,300 points, putting him behind Murray.
But Djokovic could also retain the top spot by reaching the final in Paris, which would keep him in front even if Murray wins both Vienna and Paris. If Murray can pick up 415 points in the next couple of weeks, he could contend for the top ranking at the Tour Finals, as could Djokovic if he falls back before the tournament begins.
The ATP Tour Finals offers points for each round-robin match, with additional points at stake for the other rounds.