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MONACO (AP) — Novak Djokovic looked sluggish at times and hit several unforced errors but raised his game on important points to advance to the quarterfinals of the Monte Carlo Masters on Thursday.

The top-ranked Serb, a two-time Monte Carlo champion, gained revenge over Lorenzo Musetti, who beat him last year at the Country Club in the third round. Djokovic converted five of six break points and progressed with a confidence-boosting 7-5, 6-3 win.

"I lost to him last year here. Similar circumstances," said Djokovic, who is playing in his first tournament since parting ways with former coach Goran Ivanisevic.

"I was a set and 4-2 up and then I lost the break and I must say it was in the back of my mind when I was serving at 4-2, 40-15. I lost the break of serve and I was like ‘Oh no, hopefully this is not a similar scenario like last year.' I'm really glad to overcome the challenge."

Second-ranked Jannik Sinner also advanced to the quarterfinals with a solid 6-4, 6-2 win over Jan-Lennard Struff.

Djokovic has not played much this year and is 10-3 with his best result a semifinal run at the Australian Open. He is using the Monte Carlo clay-court tournament to fine-tune his preparations for the French Open next month.

Djokovic dropped his serve immediately and struggled to adapt to Musetti's variety of shots. The Italian produced some great drop shots, was solid from the baseline and his one-handed backhands put Djokovic on the back foot.

A turning point came in the eighth game when Djokovic broke after Musetti blew a 40-0 lead. The Serb broke again in the 12th game after Musetti hit a double-fault to drop the set.

Both players struggled to hold their serves in the second set but Djokovic came out on top in the decisive points.

WATCH: Novak Djokovic gets revenge on Lorenzo Musetti in Monte Carlo | HIGHLIGHTS

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"This is clay, obviously things can turn around very quickly," Djokovic said. "A break of serve is not a big advantage on this surface as the other surfaces. We saw a little bit of a roller coaster in the second set. I'm just glad staying tough and aggressive in the right moments paid off."

Djokovic won the title in Monte Carlo in 2013 and 2015. He has not advanced past the quarterfinals since his last victory at the Country Club nine years ago.

His next opponent will be Alex de Minaur, who beat Alexei Popyrin 6-3, 6-4.

Sinner will play against Holger Rune, who defeated Grigor Dimitrov 7-6 (9), 3-6, 7-6 (2) in a three-and-a-half-hour match after fending off two match points at 5-6 in the final set.

It was Rune's second match of the day after he first completed a rain-delayed win against Sumit Nagal.

Earlier, Karen Khachanov advanced to the quarterfinals for the first time with a 6-3, 7-5 win over fellow Russian Daniil Medvedev.

Khachanov will next play two-time Monte Carlo champion Stefanos Tsitsipas, who beat Alexander Zverev 7-5, 7-6 (3).

Tsitsipas blew a 5-0 lead in the second set and failed to convert two match points before Zverev won five straight games. The Greek, however, regained his composure in the tiebreaker to improve his record against his German rival to 10-5.

Medvedev won his first clay-court tournament last year in Rome but still does not feel completely at ease on the surface. After his title in Italy, he lost in the first round to a qualifier at the French Open last season.Khachanov hit 11 winners and limited his mistakes to just three unforced errors in the second set to produce his first win over a top 5 player this season.

"First thing is to be consistent. I think lately my results have been better and better," Khachanov said. "Then to think how to beat the top guys and be at the top. These are the things that we have to keep in mind and keep working on. The win today gives extra confidence in my pocket to continue this tournament and to step into the clay swing."

It was only his second win against the fourth-ranked Medvedev.

"I lost a couple of tight matches to him on hard courts," Khachanov said. "On clay, I have not got a title yet but I have good results. Roland Garros two-time quarterfinals. Always winning matches but not winning the tournament. In a way I think overall my results on clay are better than his, maybe, and mentally he said many times he does not like to play on it."

Medvedev lost his temper near the end of the second set and was handed a point penalty after yelling at the chair umpire at the changeover. Khachanov started his final service game with a 15-0 advantage and concluded with a service winner.

Casper Ruud also made it to the quarterfinals with a 6-4, 6-2 win against Hubert Hurkacz.