Novak Djokovic and Roger Federer both advanced to the quarter-finals of the 2018 Paris Masters on Thursday with easy victories.

The Serb's third-round opponent, Damir Dzumhur, retired at 6-1, 2-1 down, and Federer beat Italy's Fabio Fognini 6-4, 6-3 in 73 minutes. 

Dzumhur was evidently struggling with a back injury throughout his clash with Djokovic and relented in the second set just after suffering a third break in his fifth service.

Djokovic will meet Marin Cilic in the last eight after the Croat defeated ninth seed Grigor Dimitrov 7-6 (5), 6-4 earlier on Thursday. 

Meanwhile, Federer will take on Kei Nishikori, who downed No. 7 seed Kevin Anderson in straight sets. 

Thursday's Results, Schedule

(5) Marin Cilic bt. (9) Grigor Dimitrov: 7-6 (5), 6-4

(2) Novak Djokovic bt. Damir Dzumhur: 6-1, 2-1 (Ret.)

 Karen Khachanov bt. (8) John Isner: 6-4, 6-7 (9), 7-6 (8)

(4) Alexander Zverev bt. (15) Diego Schwartzman: 6-4, 6-2

(16) Jack Sock bt. Malek Jaziri: 6-0, 6-4 

(6) Dominic Thiem bt. (11) Borna Coric: 6-7 (3), 6-2, 7-5 

(3) Roger Federer bt. (13) Fabio Fognini: 6-4, 6-3 

(10) Kei Nishikori bt. (7) Kevin Anderson: 6-4, 6-4

Recap

Federer, 37, is now just three wins away from his 100th career title.

His defeat of Fognini was fairly routine. He went two breaks up in the opening five games and then sealed the first set despite Fognini edging his way back into contention with a break of his own. 

In the second set Federer then saved two break points at 4-3 ahead, held for 5-3, and eased to victory with another break to love.  

What looked likely to be a swift matchup for Djokovic was wrapped up quicker than expected on Thursday due to Dzumhur's back injury, and it was clear early on the effect it was having on the Bosnian's performance.

After serving to 2-1, Dzumhur suffered back-to-back breaks in the third and fifth games of the first set. That latter game in particular took its toll on the 26-year-old, and only at the fifth time of asking did he finally give Nole his break on that occasion.

It was no surprise to see the player required attention after a game that needed 21 points to decide, per Live Tennis:

Dzumhur was showing the impact in all parts of his play and contributed four double faults en route to a first-set hiding.

The underdog started the second set just as positively as the first and successfully defended his first serve, but he finally called it a day after conceding another break soon after, via Tennis TV:

Soon-to-be world No. 1 Djokovic will return to the top of the rankings on Monday after top seed Rafael Nadal withdrew from the Paris Masters this week, as explained by tennis writer Christopher Clarey:

The Serb is bidding to return to the Paris finale for the first time since 2015, whereas Cilic has never made it to the decider.

He and Bulgarian Dimitrov warred over two sets and were rarely separated by more than one game, but Cilic got the crucial (and only) break of the second set to progress.

Djokovic will face another foe who's coping with damage, however, as tennis reporter Carole Bouchard detailed Cilic also received treatment on his way to victory:

The world No. 7 has only beaten Djokovic twice in 17 meetings, per the official ATP World Tour website, but both of those have come in their last three clashes to give Cilic some hope ahead of their quarter-final encounter.