Djokovic is in electric form heading into the Paris Masters, where he is well poised to wrestle back the No. 1-ranking from longtime rival Rafael Nadal. I come back, and it was great to be here in Paris for a couple of days.
World number one Nadal had been set to face compatriot Fernando Verdasco on Thursday (AEDT), but he announced shortly before the scheduled start time that he would not be fit to play.
The 14-time Grand Slam champion then reeled off five games in a row to end Sousa's resistance and book a meeting with Damir Dzumhur of Bosnia in the last 16.
Nadal withdrew before his quarter-final a year ago, and he must match Djokovic's performance to retain top spot going into the season-ending Tour Finals in London.More news: Affordable Care Act Marketplace open enrollment begins
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"It has been a tough year for me in terms of injuries so I want to avoid drastic things", Nadal said.
Rafa, Roger and Novak also top the list with the most number 1 players in a singles season in the last 15 years, having to go back to 2003 to find a more colorful season with Lleyton Hewitt, Andre Agassi, Juan Carlos Ferrero and Andy Roddick and conquering the top spot.
Cilic moved closer to securing one of the remaining places for the ATP Finals in London.
Federer, who has not competed in Paris at either the French Open or indoor Masters since 2015, received a standing ovation after making a winning comeback in Bercy following his late decision to compete after his 99th triumph in Basel on Sunday. "I tried. It's good to play in a relaxed manner for once, to find something in my game that could help me out for London", he said.
Fourth-seeded Alexander Zverev saved all four break points he faced in beating Diego Schwartzman 6-4, 6-2.
Croatia's Marin Cilic will play Germany's Philip Kohlschreiber after he beat Robin Haase of The Netherlands 6-7, 6-4, 6-2.