By Martyn Herman
| LONDON
LONDON Andy Murray’s climb to the top of the world rankings took a while longer than it takes thrill-seeking tourists to reach the summit of the O2 Arena roof walk. Ten years in fact.Which is why the 29-year-old Scot will be the man to beat next week as he attempts to win the ATP World Tour Finals for the first time to seal the year-end number one ranking.The distinctive domed arena next to the River Thames, home of the season-ending showpiece since 2009, has never been the happiest hunting ground for Murray.He has never made the final but knows that must change if he is to stop Djokovic from snatching back the crown.”I’ve said over the last few moths I expect Novak to start playing his best tennis again,” Murray, who boasts a 19-match winning streak, told reporters on Friday.”The last couple …