Novak Djokovic lost his temper Saturday and Rafael Nadal simply lost, spoiling a potential finals showdown at the Internazional BNL d'Italia in Rome.

The top-seeded Djokovic had an emotional outburst during his 6-3, 4-6, 6-3 quarterfinal win over German qualifier Dominik Koepfer, less than two weeks after the implosion that got him booted from the U.S. Open.

With the score tied at 3-3 in the second set after his serve was broken, Djokovic slammed his racket to the clay. He was forced to replace the mangled racket and received a warning from the chair umpire.

Earlier this week, the 33-year-old Serbian star said he had learned from the U.S. Open incident, in which an errant ball he hit in frustration struck a line judge in the throat.

"I'm working mentally and emotionally as hard as I am working physically," Djokovic said Monday. "I'm trying to be the best version of myself on the court and off the court and I understand that I have outbursts and this is kind of the personality and the player that I have always been."

Djokovic, a four-time champion in Rome, was playing in the quarterfinals there for the 14th consecutive year.

By the third set, he regained his composure, twice broke Koepfer's serve and cruised to the win.

Part of Djokovic's frustration undoubtedly was caused by his failure to convert his break point chances while Koepfer capitalized on all four of the opportunities he had. Djokovic had 21 break point opportunities -- 15 of which Koepfer fought off.

Next up for the top-seeded Djokovic is a semifinals meeting against Casper Ruud of Norway. Ruud defeated fourth-seeded Italian Matteo Berrettini 4-6, 6-3, 7-6 (5) in a three-hour match.

Ruud got the win despite Berrettini bettering him in many statistical categories on the day. Berrettini led in aces (12-4), had fewer double faults and had a greater percentage of points won on his first serve (77 percent to 75 percent).

As for Nadal, the second-seeded Spaniard's bid for a 10th title in the Italian capital ended with a stunning 6-2, 7-5 loss to No. 8 seed Diego Schwartzman of Argentina. Schwartzman had been 0-9 in his career against Nadal, losing 22 of their 24 sets.

"It was crazy. Tennis is crazy. Our performance is always crazy," Schwartzman said afterward. "The past three weeks were really bad for me. Today I played my best tennis."

Schwartzman will face 12th-seeded Canadian Denis Shapovalov, who outlasted No. 15 Grigor Dimitrov of Bulgaria, 6-2, 3-6, 6-2, for his 100th career tour-level win.

"Grigor's a player I've looked up to from juniors," Shapovalov said. "I really love the way he plays. He's beaten me twice before, so it's really nice to get the win and it's a huge step for my career."