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 later.
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.
Murray won his third title in as many weeks with victory in Vienna on Sunday, and is bidding to top the rankings for the first time.
He took the first set after breaking Muller in the sixth game and another break to go 5-4 up in the second proved crucial as the top seed won in an hour and 20 minutes.
The 12-time Grand Slam winner was in Paris for the first time since completing the career Grand Slam with a first French Open title in June, although since then his form has dipped.
Djokovic won in Toronto but lost early at Wimbledon and the Olympics, and was beaten in the US Open final by Stan Wawrinka.
Murray has closed the gap dramatically in terms of points over the past four months to trail by just 415, with 1,000 on offer to the winner in Paris.
Source: bbc sports