It didn't show in Djokovic's play, though, as he embarked upon another swing of four games in succession, holding Nishikori to three points in his next two service sets as he soared into a 4-1 lead.
After serving his way to a 2-1 lead in the third set, Djokovic ramped up his efforts and was met head-on with Nishikori's increase in tempo, but the No. 24 seed missed three break points at 2-2 and was soon trailing.
The Spaniard proved it with a daring chase-down attempt during his win over Juan Martin del Potro overnight, climbing into the stands after trying to reach a ball.
Simon, looking for his third Grand Slam quarter-final at the age of 33, secured the first break of the match to take a 4-3 lead in the second set when Del Potro netted a return.
'I don't think it would have changed if I played there a year ago, ' the 20-time Grand Slam champion said.
Khachanov's display was flashy but full of errors, and Djokovic was ruthless in punishing them, coming through 6-4 6-2 6-2 to set up a last-eight meeting with Kei Nishikori. It's a big chance for me to face Rafa.
Djokovic, victor of three singles titles at the All England Club, will next meet Japan's 24th seed Kei Nishikori. "I think he was playing more aggressive and didn't give me any free points".
Australian doctor, forerunner in Thai cave rescue, affected by family tragedy
A person with knowledge of the rescue said just before the eleventh person was spotted, that 10 people had been brought out. Rescue chief Narongsak Osatanakorn said efforts were expected "quicker or at least as quick as yesterday ".
'I'm grateful, as I said, that it was on Centre Court.
Khachanov overcame more misfortune as he held to level the third set at 2-2 despite Djokovic twice receiving the help of a net cord, but he could not survive more pressure two games later, scooping a backhand long to put his opponent on the brink.
The semi-final will be the 32nd of Djokovic's Grand Slam career but he has had to fight to get there.
'I've played this year so far only once in first four matches on Centre Court. I know how I threw the racquet.
The 12-time Grand Slam champion then raised his level in the fourth set and finished with a victor into the corner to book his place in Friday's semi-finals where he was joined by a familiar foe as Nadal won through late in the day.
"I've worked very hard and very smart to get myself in the best possible shape for the biggest events and it doesn't get any bigger than Wimbledon". I'm going to play semifinals back there again.
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