Djokovic secured his berth in quarterfinals after Damir Dzumhur was forced to pull out due to lower back pains at 2-1 down in the second set.
Djokovic, who knew on Wednesday he would be world No.1 next week after Rafael Nadal's withdrawal from the tournament through injury, was leading 6-1 2-1 when Bosnian Dzhumur retired at 6-1 2-1 after succumbing to a back problem. "And, of course, I'm very, very happy and proud about it", the Serb told reporters.
"I always believe in myself, but it was highly improbable (five months ago) considering my ranking and the way I played and felt on the court".
The 14-time Grand Slam champion had begun his pursuit of the top spot in encouraging fashion with a 7-5, 6-1 defeat of Joao Sousa on Tuesday, his 19th consecutive win.
Federer will play either Kevin Anderson or Kei Nishikori in Friday's final eight.
Apple unveils new MacBook Air with Retina Display and Touch ID
This base configuration starts at $1,199, which makes this model the cheapest, until you start adding more to the configuration. And, since the MacBook Air is "the most beloved notebook ever", according to Tim Cook, it deserved Apple's whole attention.
Cilic fired 29 winners to advance to the last eight in the French capital for the third straight year.
Djokovic and Nadal will both attempt to become five-time year-end World No. 1s at the Nitto ATP Finals, to be held at The O2 in London from 11-18 November.
Finau fights off defending champ Rose in Shanghai
Tony Finau has enjoyed such a good year that he wasn't about to let one bad break get him down Friday in the HSBC Champions . Brooks Koepka , playing his first tournament as the No. 1 player in the world golf rankings, rallied to card a 69 on Sunday.
"I am very close to London, to securing my spot mathematically", Cilic said.
Cilic, who will guarantee making the cut for London if he downs Djokovic, was ending reigning ATP Finals champion Dimitrov's season.
"It was great to be here in Paris for a couple of days and practice with the guys", said Nadal who hasn't played since the US Open.
He'll be replaced by lucky loser Malek Jaziri.
Elsewhere, German fourth seed Alexander Zverev, playing his 70th match of the season, defeated Frances Tiafoe of the United States 6-4, 6-4 while defending champion Jack Sock put out Richard Gasquet 6-3, 6-3.
With rose petals and guns, India inaugurates world’s tallest statue
At 182 meters (587 feet), the statue is more than twice the size of the Statue of Liberty in New York City. Around 3,000 workers and 250 engineers worked together to create this statue.
Austrian sixth seed Dominic Thiem reached the quarter-finals in Paris for the first time, seeing off in-form Borna Coric 6-7 (3/7), 6-2, 7-5.