PARIS – Novak Djokovic extended his massive lead at the top of the ATP world rankings, which were released on Monday, following his fourth straight victory at the season-ending World Tour Finals in London. The Serbian’s straight sets win over Roger Federer in Sunday’s final pushed his advantage over world number two Andy Murray to almost 8,000 points. British No 1 Murray is guaranteed to finish the year No 2 for the first time, which should give him the second seeding at January’s Australian Open. The top 20 was otherwise unchanged with Federer only 405 points behind Murray, Stan Wawrinka at No 4 and Rafael Nadal retaining fifth spot. Czech Tomas Berdych is at No 6, Spanish David Ferrer No 7, Japanese Kei Nishikori No 8, French Richard Gasquet No 9 and French Jo-Wilfried Tsonga at No 10.