The 31-year-old Spaniard, who needs to win in Monte Carlo to prevent his perennial rival Roger Federer regaining the world number one ranking, required an hour and 38 minutes on his favourite clay surface to defeat the 21-year-old world number 38.

Nadal is now due play Austrian fifth seed Dominic Thiem, who beat 12-times Grand Slam winner Djokovic 6-7, 6-2, 6-3 at the Monte Carlo Country Club in this ATP Masters 1000 event..

The Serb has not won a Grand Slam title since the 2016 French Open and has failed to reach the last eight in any of his four tournament appearances since making his return following an elbow injury.

"Ideally, I'd want to be playing the way I played for so many years, but obviously patience is required," Djokovic, who confirmed he will play in either Budapest or Barcelona next week as a wildcard, said. 

"I really believe if I continue doing what I'm doing, believing in myself, I know eventually I'm going to get there."

Djokovic, who has slipped to 13th in the rankings, showed glimpses of his best form against Thiem, whom he described as a "top-three player in the world on clay".

The 12-time Grand Slam champion saved three set points at 5-2 down in the first, breaking back to level at 5-5 and taking the tie-break with his first set point.

However, he was outclassed in the second set and seemed to fade in the decider, Thiem claiming his first break point for 4-3 and taking Djokovic's serve again to win after almost two and a half hours.

Thiem, 24, lost his first five meetings with Djokovic before beating him 7-6, 6-3, 6-0 in last year's French Open. 

Elsewhere, third seed Alexander Zverev beat fellow German Jan-Lennard Struff 6-4, 4-6, 6-4, but missed out on a meeting with his older brother Mischa, who lost to France's Richard Gasquet.

Gasquet, 31, earned his 500th Tour victory with a 6-2, 7-5 win.

Belgian sixth seed David Goffin won 6-4. 7-5 against Spain's Roberto Bautista Agut to book a quarter-final against Bulgarian fourth seed Grigor Dimitrov, who beat Germany's Philipp Kohlschreiber 4-6 6-3 6-4.

Canada's Milos Raonic pulled out of his last-16 match against Croatian second seed Marin Čilić because of a knee injury.