But then, the Serb has long appeared comfortable on Wimbledon's Centre Court, where he has won seven of his 24 grand slam titles.
He was certainly more at home than Czech qualifier Vit Kopriva who was blown away 6-1 6-2 6-2 in less than two hours.
Djokovic wore a grey support on his right leg for which he had received special permission after promising to try and source a white one.
"I know it's not ideal. I like to go all white and I like to respect the rules," he said.
Russian Andrey Rublev fell to a shock Wimbledon defeat to grand slam debutant Francisco Comesana. (AP PHOTO)
"I'm very pleased with the way I felt on the court," Djokovic added. "Obviously coming into this year was different because of the knee, and didn't know how everything would unfold on the court. I'm extremely glad about the way I felt and the way I played.
"I tried to really focus on the game and not think too much about the knee. I've done everything possible in the last three-and-a-half weeks. If it was any other tournament I probably wouldn't have risked it - but I love Wimbledon."
Having dismissed the 123-ranked Kopriva, Djokovic now plays British wild card Jacob Fearnley who was ranked outside the top 500 until he won an ATP Challenger event as a qualifier last month.
It was also a straightforward afternoon for fourth seed Alexander Zverev who eased to a 6-2 6-4 6-2 victory over Roberto Carballes Baena under the closed roof of Court One.
Zverev has never gone past the fourth round at Wimbledon, his worst record at a Grand Slam. However, he believes this time could be different.
Alexander Zverev plays a backhand return during his win over Roberto Carballes Baena of Spain. (AP PHOTO)
"I've struggled over the years, unfortunately, but I feel different this year, somehow much more into it and more alive on these courts," Zverev said.
"For some reason, very early in my career I decided that I hate grass courts, then for some reasons this year, I decided that I love them. That is the biggest change.
"I also feel this is the most open Wimbledon in 20-plus years. We had great champions like (Roger) Federer, (Rafael) Nadal, Djokovic, (Andy) Murray and it was always between them.
"If somebody has two great weeks then they can do great things. I hope, for once, it is going to be me."
One man it will not be is No.6 seed Andrey Rublev, who lost to Francisco Comesana, an Argentine who was making his main draw grand slam debut.
The 23-year-old, ranked 122nd, won 6-4 5-7 6-2 7-6 (7-5) in just under three hours.
Rublev, who last year reached the quarter-final, screamed out loud, ranted at his courtside coaching team, and smashed his racket repeatedly over his knee, leaving it bloody and bruised for the rest of the match.
The combustible Russian explained he did that to avoid a code violation for hitting his racquet against the ground.
"I would not do it if I was able to hit the racket on the floor," he said with clear logic.
"I don't know why in that moment, I couldn't take it any more. I needed to let emotions out."
Seventh seed Hubert Hurkacz, Stefanos Tsitsipas, seeded 11 and 15th-seed Holger Rune progressed.
Earlier, two-time Wimbledon champion Andy Murray pulled out of what would have been his final singles appearance at the event.
Due to a back injury he will now only play doubles with his brother Jamie, with their first opponents later this week being Australian duo Rinky Hijikata and John Peers.
with agencies
