PARIS (Reuters) - Novak Djokovic began his bid to hold on to his number one ranking with a 6-3 6-4 win over Luxembourg's Gilles Muller in the second round of the Paris Masters on Wednesday.
The Serbian, who could be dethroned from the top spot by Wimbledon champion Andy Murray this week, broke Muller once in each set to secure a drama-free victory.
The 29-year-old will hold on to his ranking if he reaches the final in Paris.
Murray plays Spaniard Fernando Verdasco later on Wednesday.
Japan's Kei Nishikori cruised into the third round with a 6-2 7-5 win over Serbian Viktor Troicki as the race for places at the ATP Tour Finals gathered pace.
The fifth seed, one of six players to have already qualified for the season-ending finals in London, breezed through the first set and quickly broke in the second.
A lapse in concentration by the Japanese, however, allowed world number 28 Troicki to break back but Nishikori broke again to end the contest in straight sets.
He will next face either local favourite Jo-Wilfried Tsonga, the 11th seed, or Albert Ramos-Vinolas of Spain.
Croatian Marin Cilic set up a third-round clash with Belgium's David Goffin as both battle for one of two remaining spots for the Nov. 13-20 ATP event at the 02.
Cilic, ninth in the Race to London, beat compatriot Ivo Karlovic 7-6(7) 6-2 while Goffin, who is 11th with an outside chance of qualifying, beat France's Nicolas Mahut 7-6(5) 6-3.
Dominic Thiem's chances of taking part in the London showdown, took a big blow when the Austrian, eighth in the Race, lost 6-2 6-4 to American Jack Sock in the second round in Paris.
Former world number one Rafa Nadal is seventh in the Race but has ended his season and will not play in the Tour finals.
(Reporting by Julien Pretot; Editing by Ed Osmond)