Rafael Nadal withdrew from the Paris Masters after an abdominal injury preventing him from the second round face-off with compatriot Fernando Verdasco.
This automatically takes in-form Serbian Novak Djokovic to the top spot in the rankings for the first time in two years.
On a day of drama, the third seeded Roger Federer advanced to the third round by a walk-over when his scheduled opponent, Milos Raonic could not compete due to injury.
Earlier, Grigor Dimitrov of Bulgaria defeated Spain’s Roberto Bautista Agut 7/6 (10: 6/4 while Alexander Zverev marched on with a 6/4; 6/4 victory over America’s Frances Tiafoe.
John Isner outlasted Kukushkin of Kazakhstan in a marathon 6/3; 6/7 (2); 7/6 (1) marathon in which the American’s service power determined the outcome.
Kei Nishikori continued his consistent winning ways in defeating Adrian Mannarino 7/5; 6/4. Marin Cilic kept his London quest alive with a quick 6/3; 6/4 win over Germany’s Philip Kohlschreiber.
The second seeded Djokovic had no idea that his second round victory over Portugal’s Jaoa Sousa would propel him to the top spot when the news of Nadal’s withdrawal spread through the venue.
Nadal has never won this indoor hard-court tournament; despite his eleven victories in the Grand Slam of a city he described the most important in his professional career.
The beneficiary of Nadal’s withdrawal was Tunisia’s Malek Jaziri who had lost in the final qualifying round and was pulled out as the lucky loser.