Britain's Andy Murray holds up the ATP World No 1 trophy following his win over Novak Djokovic of Croatia in the men's singles final at the ATP World Tour finals tennis tournament at the O2 Arena in London, Britain, Nov 20, 2016. [Photo/IC]

LONDON -- Andy Murray beat fourt-time defending champion Novak Djokovic in straight sets at London's O2 Arena on Sunday to win the ATP World Tour Finals title and also secure year-end No 1 in the world rankings.

The 29-year-old became the 17th different player to finish the year atop the world in history since 1973 and the first British player to achieve the feat.

The Scot extended his winning streak to 24 matches dated back to Sept 18 after a 6-3, 6-4 victory.

Murray had spent nine hours and 56 minutes entering the final, including the two longest best-of-three set matches in tournament history, while Djokovic needed three hours less to reach the title match.

The Briton managed to break Djokovic at 3-3, held his own and broke again for a 5-3 lead in the first set. He then served for the set 6-4 after Djokovic had made it 5-4.

Murray became stronger and more accurate as Djokovic constantly made unforced errors. He soon took a 4-1 lead and fought off a surge from the five-time champion, who cut the deficit to 4-3.