Djokovic, who was seeded third and received a first-round bye, was playing his first match since limping out of his Australian Open semi-final in January.
But the Serb said that while he was not 100 per cent, fitness was not the issue.
“I was outplayed by just a better player today,” he said.
“Yes, I wasn’t at my desired level, and it could be that I’m still not moving the way I want to move, but I played without pain, so there is no excuse in that.”
“I think he played a masterclass match to be honest, tactically, and served very well, so just a very deserved win from his side.”
It was only Berrettini’s second win this year and his first over a player in the top 10 since 2023.
It was also the Italian’s first ever win over Djokovic. Their previous encounters included victories for the Serb in the Wimbledon final and Roland Garros quarterfinals both in 2021.
“Something I’ve been looking to do for a long time. I’ve played against him in the most important tournaments on tour,” the 28-year-old Italian said on court after the victory. “I wish I could have won one of those matches.”
Berrettini has struggled with injuries over the last 18 months but won three tournaments after returning to court last year.
“Really happy with my performance,” he said. “Really happy because I enjoyed my time out there, which is the most important thing.”
The first set went with serve but Berrettini took two points off Djokovic’s serve to win the tiebreak. The Italian then broke to love in the second game of the second set.
Djokovic had broken Berrettini 27 times in their four previous encounters but the Italian was comfortable on serve until the final game before finally winning on his second match point.
“A champion like Novak is always ready to come back,” Berrettini said. “You don’t have to think about match point. You have to think about the next point.”
