Britain's Andy Murray is two wins from becoming world number one following Novak Djokovic's surprise defeat by Marin Cilic at the Paris Masters.
Djokovic needed to reach the final to retain the top ranking but lost 6-4 7-6 (7-2) to Cilic in the quarter-finals.
Second seed Murray must beat Tomas Berdych and either Jo-Wilfried Tsonga or Milos Raonic to become world number one for the first time.
The Scot, 29, plays Czech seventh seed Berdych later on Friday.
Frenchman Tsonga then takes on Canada's Raonic in the last of the quarter-finals.