Djokovic, 36, who was beaten by eventual winner Jannik Sinner in the semi-finals of the Australian Open, is yet to win a tournament this year.

"No titles this year. That's not something I'm used to," said the Serb, who hit 17 winners but made nine unforced errors.

"I was starting the season most of my career with a Grand Slam win or Dubai win. It's fine. It's part of the sport. You just have to accept it. Some you win, some you lose.

"Hopefully I'll win some more and still keep going. I guess every trophy that eventually comes my way is going to be great, to break the kind of negative cycle a little bit I'm having in the last three, four tournaments where I haven't really been close to my best."

Nardi, who was beaten by Belgium's David Goffin in the final round of qualifying, said it was an "amazing feeling".

"I couldn't even imagine to play a match against him, and now I also beat him," he added.

"It's such a dream come true for me. After the match, my coaches told me, Luca, everyone was cheering for you. Incredible. Against Djokovic, he's the best player ever.

"I will keep it, this moment, for the rest of my life."

Nardi will play Tommy Paul in the last 16, with the American progressing courtesy of a 6-4 6-4 win over France's Ugo Humbert.

Daniil Medvedev beat Sebastian Korda 6-4 5-7 6-3 and will play Grigor Dimitrov in the next round.

Holger Rune, Casper Ruud and Taylor Fritz also made it through to the last 16.