Asked if it was the angriest he's ever been on a court, he replied: "Yes, it could have been."
Besides pulverizing the racket, Nishikori also complained about the "heavy balls," and the "high bounces" on the surface in Rio as his trip around the Latin American clay circuit ended quickly.
The No. 5-ranked Nishikori reached the final last week in Buenos Aires, losing to Alexandr Dolgopolov of Ukraine. It was his sixth straight loss in a final since winning the Memphis Open a year ago.
"I think the ball was the most difficult to adjust to," he said. "I couldn't do anything today."
It was a different story for Bellucci, the home country favorite who pulled a huge upset during Carnival week in Brazil.
"You don't see Kei break the racket often," Bellucci said.
The No. 75-ranked Bellucci had lost his previous two matches against Nishikori, including a three-set loss two years ago in the first round of the French Open.