Roger Federer made a comfortable start to his quest for a 100th title, dispatching Fabio Fognini in straight sets. "I'm obviously not happy to see him [Nadal] being injured and pulling out from the tournament in this final race for top rankings".
Djokovic can regain top spot from Rafael Nadal this week if he betters the Spaniard's performance in the French capital, where the Serb is a four-time victor of the indoor tournament.
The Serbian, who will return to world number one next week, was 6-1, 2-1 up when a back injury got the better of his Bosnian opponent.
Federer will play Canada's Milos Raonic on Wednesday after receiving a bye in the first round. Djokovic was in total control and did not face a break point, breaking Dzumhur's serve three times.
With his 42nd win of the season, the 28-year-old booked a quarterfinal match Friday against 20-time Grand Slam champion Federer, whom he has beaten only twice in eight attempts.
"I feel like it's better for me to play matches rather than practice", Federer said.
Rafael Nadal's withdrawal from the Paris Masters has put his participation at the 2018 ATP Finals in doubt. I checked with the doctor and he said that he recommended to not play, because if I continued the abdominal may break and could become a major thing. He beat Nadal in a Wimbledon semi-final thriller before ending a two-year Grand Slam drought by defeating Kevin Anderson in the final.
Pentagon ramps up military activity across border before midterms
The U.S. military has already begun delivering jersey barriers to the southern border in conjunction with the deployment plans. About 600 migrants in the second group tried to cross a bridge from Guatemala to Mexico en masse Monday.
Seeking a record-equalling 33rd Masters and record-extending fifth Paris title, Djokovic will face a much more challenging test in the last eight against Marin Cilic.
Cilic trailed 5-4 during the tiebreaker but won both points on Dimitrov's serve before serving out the first set.
The win improved the Croat's prospects of making the ATP Finals in London starting Nov 11.
"I am very close to London, to securing my spot mathematically", Cilic said.
Djokovic has won 15 of 17 against Cilic but they have split two meetings this year.
Thiem, on pace to qualify for the Finals, rallied past the Shanghai Masters finalist Borna Coric 6-7 (3), 6-2, 7-5.
The Russian will next play Alexander Zverev after the German fourth seed beat Diego Schwartzman of Argentina 6-4, 6-2.