The giant American saved four match points before the 22-year-old Khachanov, who had already staved off two himself, finally threaded a backhand victor past the net-rushing Isner to win after almost two-and-a-half hours of massive hitting.
Djokovic revealed he also was not feeling very well out on court. "After that, I couldn't get any points on return, so I took some risks and played more aggressive, and I did it".
"But I haven't been really reflecting on that and I haven't been really focusing on that too much because it's the middle of the week". Second seed Djokovic is a four-time champion in Paris and is bidding to reclaim the world number one ranking from Rafael Nadal this week.
Nadal has been out of action for over two months, which has allowed Novak Djokovic to close in on him in the ATP singles rankings. But Djokovic was in total control and did not face a break point, breaking Dzumhur's serve three times.
Cilic, the fifth seed, secured his quarter-final ticket with a 7-6 (7/5), 6-4 victory over Grigor Dimitrov. Round 3 may bring the ever-improving power player, Karen Khachanov, and this quarter is topped by Alexander Zverev, whose debut here a year ago ended in the second round. He led 6-2, 2-0 against Matthew Ebden when the Australian retired.
If he wins in Paris, he will equal Nadal's record of 33 Masters titles and he can also extend his record number of triumphs at the French capital's indoor event to five.
"I have to think longer term".
There was a more stressful passage for Isner, but the American did just enough to edge out Mikhail Kukushkin 6-3 6-7 (2-7) 7-6 (7-1) and keep his hopes of an ATP Finals place alive. But the third-ranked Federer feels comfortable with it.
Speaking about how he has been coping with his injury and long break from tennis, Nadal said-"It's nothing new for me".
"I'm aware of what's happening and it's sad".
The day started with schedule matches and players moving to the third round; with the top seeds playing their first match having drawn byes into the second round. I've always been trying to be very professional and respectful towards people I have commitments with.
The Spaniard, for all his success at Roland Garros, has never lifted the trophy at the Paris Masters - his best showing came when he lost the 2007 final to David Nalbandian.
"I rarely play two or three tournaments in a row now".
"It was welcome because my body needed it", Federer said.