"I've been building the last couple of weeks on the level of tennis that I've played the last couple of month, the last couple of clay-court tournaments and Queen's".
The three-time champion made minor errors in the first set but managed to convert three break points on his way to a comfortable victory.
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.
"I thought it was unnecessary to get the warning", Djokovic said as he came off court. "In the midst of emotions in a tough match, it happens".
But the second seed stayed alive by taking the fourth set before the gripping drama continued in an electrifying deciding set in which both players were left diving after volleys and slipping over as they chased after blinding winners.
Scot Murray, 32 - who triumphed here previous year alongside Martina Hingis - and former singles world No.1 Azarenka moved into the quarter-finals with a 7-6 (8-6), 6-3 win over Matwe Middelkoop and Johanna Larsson.
A nagging elbow injury caused him to take an eight-month break from the sport prior to last year's US Open, and he also admitted to having to deal with personal issues.
'I feel like I'm peaking at the right moment.
It is Djokovic's first appearance in the semi-finals at the All England Club since 2015 - when he last won the title - and he revealed his motivation is fully back as he chases Grand Slam title No. 13.
"You're saying in the point if I toss my racket like this I'm ruining the court?"
He came into the match having won 32 consecutive sets at Wimbledon, a run he stretched to 34 before faltering.
"I feel great to be in the last four of Grand Slam", beamed the Serb afterwards.
Rafael Nadal awaits in the semifinals after the Spaniard took the scenic route in a five-set marathon against Juan Martin del Potro; a rematch of the 2011 contest where Djokovic first tasted success on the lawns of south west London. It was a step up in momentum that Nishikori momentarily halted with a break at the start of the fourth, but Djokovic then returned the favour and closed out the match.
"He claims that he didn't see what Nishikori has done, but apparently he always sees what I do", Djokovic said afterward, "something that I don't think is fair".
"I want to use today's result as a spring from which to aim for a final place".