Geoff Burke-USA TODAY Sports

No. 15 seed Karen Khachanov took down No. 4 Daniil Medvedev 6-3, 7-5 in an all-Russian Round of 16 match at the Rolex Monte Carlo Masters on Thursday in Monaco.

Medvedev got into a heated exchange with an umpire late in the match, when he led the second set 5-4 and served for set point. Khachanov fought back to win the game, but Medvedev was upset that a line judge made an apparently incorrect call on one of the points.

Medvedev was assessed a point penalty for throwing his racket and yelling for the umpire to "Open your freaking eyes."

"Mentally, even though I've lost a few hard matches to him on hard courts, I know he doesn't like to play on clay and that gives me some extra confidence," Khachanov said in his on-court interview.

"Sometimes I know Daniil can lose his mind. Sometimes he uses it as a tool, but it can get out of control sometimes. I tried not to look at him or focus on him, and just serve it out."

The fifth seed also bowed out Thursday, as No. 12 seed Stefanos Tsitsipas of Greece edged Germany's Alexander Zverev 7-5, 7-6 (3). Tsitsipas and Khachanov will meet in the quarterfinals.

No. 1 seed Novak Djokovic dispatched Italian Lorenzo Musetti 7-5, 6-3, avenging an upset loss to Musetti in the same round of Monte Carlo last year. The Serbian broke Musetti five times in six opportunities on Thursday.

"I don't think I am still at my top level but it was a great test today against a great player, a very talented player," Djokovic said. "I lost to him last year here, similar circumstances. I was a set and 4-2 up and I must say it was in the back of my mind when I was serving at 4-2, 40/15 and lost my serve today. I thought, ‘Oh no, hopefully this is not similar scenario like last year.' I am really glad to overcome the challenge and look forward to the next one."

No. 11 seed Alex de Minaur will be waiting for Djokovic in the quarters. He defeated fellow Australian Alexei Popyrin 6-3, 6-4 in the Round of 16.

No. 7 seed Holger Rune finished off a 6-3, 3-6, 6-2 win over India's Sumit Nagal that had been suspended due to rain Wednesday. Rune then went on top No. 9 seed Grigor Dimitrov of Bulgaria 7-6 (9), 3-6, 7-6 (2) in three hours and 30 minutes, making for an especially long day.

"I had a match earlier today which was two sets, so I played five sets today actually, which is pretty brutal," said Rune, who saved two match points in the third set. "To beat Grigor, who's played such a good season, and last season, and to get my revenge is a great feeling. I played very good and I'm happy to beat him."

No. 2 seed Jannik Sinner of Italy breezed past German Jan-Lennard Struff 6-4, 6-2; No. 8 seed Casper Ruud of Norway took down No. 10 Hubert Hurkacz of Poland 6-4, 6-2; and No. 14 seed Ugo Humbert of France rallied past Italian lucky loser Lorenzo Sonego 5-7, 6-3, 6-1.

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