ROME -- Less than two weeks after getting defaulted from the US Open, Novak Djokovic lost his cool again midway through a 6-3, 4-6, 6-3 win over German qualifier Dominik Koepfer in the Italian Open quarterfinals Saturday.
When Djokovic was broken at love to even the second set at 3-3, he slammed his racket to the red clay in anger.
With the frame broken and the strings mangled, Djokovic was forced to get a new racket and received a warning from the chair umpire.
"It's not the first nor the last racket that I'll break in my career," Djokovic said. "I've done it before and I'll probably do it again. I don't want to do it, but when it comes, it happens.
"That's how, I guess, I release sometimes my anger and it's definitely not the best message out there, especially for the young tennis players looking at me, and I don't encourage that -- definitely."
Top-ranked Djokovic was thrown out of the US Open for unintentionally hitting a line judge in the throat with a ball in a fit of anger.
At the Foro Italico, Djokovic had already appeared frustrated during the match before he broke his racket, glaring toward the umpire following a couple of overrules and a point that was ordered to be replayed.
"That's just me," Djokovic said. "Of course, I'm not perfect and I'm doing my best."
The 97th-ranked Koepfer, who screamed at himself in frustration throughout the match, was also warned for misbehavior early in the third set.
Aiming for his fifth title in Rome, Djokovic will face Casper Ruud in the semifinals. Ruud eliminated local favorite Matteo Berrettini 4-6, 6-3, 7-6 (5) in a match that lasted 2 hours, 57 minutes.
Ruud is the first Norwegian to reach the semifinals of a Masters 1000 tournament. His father, Christian Ruud, got as far as the quarterfinals of the Monte Carlo Masters in 1997.
While fans have not been admitted to the tournament yet -- Italy's sports minister said Friday that 1,000 spectators will be allowed in for the semifinals and final -- workers, family members and other onlookers inside picturesque Pietrangeli Stadium provided some support for Berrettini, who is from Rome.
Nicola Pietrangeli, the 1957 and 1961 Rome champion and the man the stadium is named after -- was also among those sitting in the white marble stands.
"There would have been a lot more adrenaline with fans," Berrettini said
The Associated Press contributed to this report.