ROME -- Novak Djokovic knows it isn't model behaviour when he loses his cool on the tennis court.

Yet he just can't help himself.

Exactly two weeks after he was defaulted from the U.S. Open, and a day after he was warned by the chair umpire for breaking his racket in a fit of rage, Djokovic received an obscenity warning midway through a 7-5, 6-3 win over Casper Ruud in the Italian Open semifinals Sunday.

The obscenity came in the third game of the second set, by which time Djokovic had a running dialogue with the chair umpire over a series of contested calls.

"I deserved the warning," Djokovic said. "I didn't say nice things in my language.

"I had a couple of disputes with the chair umpire with those calls," Djokovic added. "As I understood, I was three out of three right, but doesn't matter. Everybody makes mistakes. It's fine. It was a kind of the heat of the battle. There is a lot of intensity on the court. A lot of pressure for him, for both players. It's kind of whatever happens, happens."

As opposed to his previous two outbursts, this time there were fans in the stands who could clearly hear how Djokovic dealt with his frustration.

With 1,000 spectators allowed in to the Foro Italico for the first time this week, a large proportion of those in attendance were children.

"I don't want to do it, but when it comes, it happens," Djokovic said Saturday. "That's how I, I guess, release sometimes my anger. And it's definitely not the best message out there, especially for the young tennis players looking at me. I don't encourage that -- definitely."

Ruud was Nick Kyrgios' opponent during last year's Italian Open when the Australian walked off the court and threw a chair onto the red clay, leading to him being defaulted and fined.

"Some players, or especially Djokovic, (are) very passionate," Ruud said. "Some players just by nature can show more emotions than other ones. That's part of the game."

Djokovic's behaviour once again overshadowed his performance, in a match where he had to save two set points when Ruud served for the first set at 5-4 -- one of them with a delicate backhand drop-shot winner.

The top-ranked Djokovic also served five aces in a single game to take a 6-5 lead in the first.

Ruud, 21, the first Norwegian player to contest a Masters 1000 semifinal and a product of Rafael Nadal's academy, put up plenty of resistance and also produced the shot of the day: a leaping over-the-shoulder hook shot for a winner as he raced back to chase down a lob -- earning a thumbs-up from Djokovic.

"He has that pattern of play on clay with a lot of spin," Djokovic said. "I'm sure we will see more of him in the big tournaments, especially on this surface. He's got the game."

Djokovic improved to 30-1 this year. His only loss came when he was thrown out of the U.S. Open for unintentionally hitting a line judge in the throat with a ball during his fourth-round match against Pablo Carreno Busta.

In Djokovic's 10th Rome final -- he has won four -- he"ll face either eighth-seeded Diego Schwartzman or 12th-seeded Denis Shapovalov.

Schwartzman beat nine-time Rome champion Nadal late Friday.

In the women's final, top-seeded Simona Halep will face second-seeded Karolina Pliskova, the defending champion.

Halep reached her third Rome final by beating Garbine Muguruza 6-3, 4-6, 6-4 to improve her record in tennis' restart to 9-0. Pliskova defeated fellow Czech and last year's French Open finalist Marketa Vondrousova 6-2, 6-4.

Muguruza struggled with her serve and double faulted on the final two points of the 2 hour, 16-minute match.

Halep lost to Elina Svitolina in the 2017 and 2018 finals.

"I'm not playing (Svitolina), so I have a plus," Halep said. "I have just to manage it a little bit better than previous years. ... Now I'm more mature. So let's hope that I can be better tomorrow and to win it."

The second-ranked Halep is 13-0 overall stretching back to February, when she won a title in Dubai. After the tour's five-month break due to the coronavirus pandemic, the Romanian returned by raising another trophy in Prague last month. She then skipped the U.S. Open due to travel and health concerns.

Pliskova dictated play against Vondrousova with her serve, hitting six aces to Vondrousova's one and saving five of the seven break points she faced.

The French Open starts next weekend.