Andy Murray will begin his Paris Masters campaign against Fernando Verdasco, while Novak Djokovic was in unfamiliar doubles action on Monday.
Murray can overtake Djokovic at the world rankings' summit if he claims a maiden title in the French capital, as long as the Serbian is not the beaten finalist.
The Scot, enjoying a bye to the second round, will meet world number 46 Verdasco, who overcame Robin Haase.
Djokovic, meanwhile, featured in the doubles alongside compatriot Nenad Zimonjic, although the pair went down in straight sets to Quentin Halys and Adrian Mannarino.
The 12-time major winner will hope that is not a sign of things to come as he looks to make it four successive triumphs at this tournament and defend his number one spot.
VERDASCO IN CONTROL BEFORE HAASE'S HIP GIVES OUT
Verdasco did not even have to play two full sets to get past Dutchman Haase and advance to his clash with Murray.
After a pair of breaks gave him the opening set 6-2, Verdasco was about to serve for a 4-2 lead in the second when his opponent retired hurt with a hip problem.
DJOKOVIC DUMPED OUT IN THE DOUBLES
It was an unfamiliar first-round exit for Djokovic, as he and Zimonjic went down 6-3 6-4 to Halys and Mannarino.
Perhaps using the contest as a warm-up for his singles campaign, one would expect Djokovic to return to winning ways when he meets Nicolas Almagro or Gilles Muller in the second round.
If Djokovic is triumphant at this tournament, he will become only the third man to win both the French Open and the Paris Masters in the same year, and the first since Andre Agassi in 1999.
There were wins for Pablo Carrena Busta, Steve Johnson, Joao Sousa and Marcos Baghdatis in round one.
Paolo Lorenzi, Gilles Simon, Jan-Lennard Struff and Albert Ramos-Vinolas also progressed to the second round.