Novak Djokovic beat Gilles Muller 6-3 6-4 in the Paris Masters second round as he fights the challenge of Andy Murray for his world number one status.
Djokovic easily saw off his 34th-ranked opponent from Luxembourg to set up a clash with Bulgarian Grigor Dimitrov.
Briton Murray, who could overtake the Serb with a good run this week, faces Fernando Verdasco from about 18:30 GMT.
Djokovic, 29, has been top for 122 weeks and will hold on to his ranking if he reaches the final in Paris.
However, failure to do so would allow Murray to overtake him if the Scot can win, or if Murray reaches the final and Djokovic exits before the semis.