The former top-ranked Serb lost to Dominic Thiem 6-7 (2), 6-2, 6-3 Thursday in the third round of the Monte Carlo Masters despite saying recently he was finally playing pain-free after two years of struggles with a persistent right elbow injury.

Djokovic saved one match point against Thiem, but indecision appeared to cost him on the second. The ninth-seeded Djokovic seemed to change his mind about which shot to play, initially shaping up for a low backhand volley at the net but instead going for a backhand that went long.

Djokovic did save three set points in the first set, and the momentum carried over into the tiebreaker. But his backhand let him down after that, with Thiem getting consecutive breaks and holding for the second set when Djokovic patted a two-handed backhand into the net.

Still, after so much injury frustration, Djokovic was encouraged about coming through three matches without any relapse.

"I played without pain, which is important," said Djokovic, who says he will play at the Barcelona Open or Hungarian Open next week. "I'm really happy with the way things are working out right now with the elbow."

Thiem, who also beat Djokovic on clay in last year's French Open quarterfinals, will next face defending champion Rafael Nadal.

The top-ranked Nadal beat big-hitting Russian Karen Khachanov 6-3, 6-2 on Friday to reach the quarterfinals, clinching the victory with a clinical smash at the net.

Nadal's victory could have been even more efficient, but he surprisingly dropped his serve in the seventh game of the first set. He broke straight back and then took complete control.

Thiem can take confidence from having beaten Nadal twice on clay, including in the quarterfinals of last year's Rome Masters.

"It's a way better feeling if you go against him and know that you've beaten him already on this surface," Thiem said. "It's the ultimate challenge to play against him. I have to raise my level again."

Third-seeded Alexander Zverev missed out on facing his older brother in the last eight after beating Jan-Lennard Struff 6-4, 4-6, 6-4. Mischa Zverev lost 6-2, 7-5 to Frenchman Richard Gasquet.

Second-seeded Marin Cilic advanced without hitting a ball after Milos Raonic pulled out with a right knee injury. Cilic, the Australian Open runner-up, will next play Kei Nishikori of Japan, who beat Andreas Seppi 6-0, 2-6, 6-3.

Raonic said he hurt his knee during his second-round win on Wednesday.

"It was difficult yesterday early in the match, I rotated on my knee. I thought through treatment and so-forth it would be better," Raonic said. "I was predisposed to some risk and I was unable to play with that amount of pain. I'll know more in the [coming] days."

Sixth-seeded David Goffin also made it through after beating Roberto Bautista Agut of Spain 6-4, 7-5 in a match that included a bizarre incident involving a ball boy.

After dropping his serve to trail 4-1, Bautista Agut cleared a ball from the back of the court just as a ball boy was sprinting across. The ball, which was traveling slowly, bounced and clipped the ball boy on the head. Bautista Agut raised a hand in apology but still got a warning from the chair umpire. He was also fined 2,500 euros ($3,100) for unsportsmanlike conduct.

Goffin, a semifinalist in Monte Carlo last year, was confused by what happened.

"I just saw the ball directly hitting the ball boy. I was surprised to see he [Bautista Agut] only got a warning," Goffin said. "For me, if you send a ball onto the ball boy's head, you're [kicked] off. I don't know what the rules are exactly, how he only got a warning. He said the ball bounced and the ball boy just happened to be there. Bad luck for him. But in any case, it's just an incident."

Goffin will next play Grigor Dimitrov in their first meeting on clay. The fourth-seeded Bulgarian beat Philipp Kohlschreiber 4-6, 6-3, 6-4.