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.
Djokovic wrested back the momentum for good after coming from 0-40 down at 2-2 in the third set to hold serve, and then breaking his Japanese opponent in the next game.
Djokovic's last run to the final four at Wimbledon ended with him winning the tournament - and he then went on to lift the 2015 US Open and 2016 Australian and French Open titles, becoming only the third man to hold all four Grand Slam trophies at the same time.
Seeded 12, Wednesday will Djokovic's 41st appearance in a Grand Slam quarter-final. "I'm a different person, different player today".
"I'm not sure what to say right now", U.S. Open finalist Anderson said.
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He added: 'With the performances I've had, I deserve to be in the semi-finals. I think confidence is back for him.
Novak Djokovic felt he was a different player to the Wimbledon victor of old but comparisons were inevitable on Wednesday as the Serb rolled into the semi-finals for the first time since 2015. "I didn't harm the grass", he said. During Wimbledon, speaking of the big event that is taking place in Russian Federation, in which his country, Serbia, failed to go beyond the group stages, Djokovic said: 'I support Croatia. But there was no stopping the Serb once he made it on to Court One as he romped to a 6-4 6-2 6-2 win to reach the quarterfinals for a 10th time.
"It took me two or three months and that was frustrating that I wasn't able to perform the game that I was used to and the level of tennis I wanted to play".
"It motivates me to do extremely well here because I don't want to sit here and explain my loss".
"After that he was playing better". Despite handing back an early break in the opening set, Djokovic broke again for 5-3 and then wrapped up the set.
Djokovic will face old rival and world No. 1 Nadal, who saw off Del Potro 7-5, 6-7 (7-9), 4-6, 6-4, 6-4 after 4 hours and 48 minutes on Centre Court to reach his sixth Wimbledon semifinal and 28th at the majors.