Playing his second tournament since parting company with his entire coaching team, Djokovic broke once to take the first set but dropped serve in the second before wrapping up victory.

Djokovic still needs to convince having suffered a heavy defeat to Rafael Nadal in Madrid last week and struggled past Britain's Aljaz Bedene in the previous round.

And he will get the chance in the quarter-finals when he faces Argentina's in-form Juan Martin del Potro, who was an impressive 7-6 (7/4) 6-3 winner over seventh seed Kei Nishikori.

John Isner defeated third seed Stan Wawrinka 7-6 (7/1) 6-4 to set up a rare clay-court quarter-final against sixth seed Marin Cilic, who beat David Goffin 6-3 6-4.

Fifth seed Milos Raonic overcame Tomas Berdych 6-3 6-2 and will face Alexander Zverev, a 6-3 6-3 winner over Andy Murray's conqueror Fabio Fognini, in the last eight.

Nadal extended his current winning streak on clay to 17 matches with a 6-3 6-4 win over American Jack Sock in their quarter-final.

Nadal's recent surge has seen him clinch consecutive titles in Monte Carlo, Barcelona and Madrid, and he is now three wins away from an eighth Rome crown.

The Spaniard was in a clinical mood against Sock, converting all three of the break points he fashioned on his opponent's serve to triumph in exactly 80 minutes.

In the last eight Nadal will face Dominic Thiem, whom he has beaten in back-to-back finals in Barcelona and Madrid.

The eighth-seeded Austrian was forced to save three match points before battling to a 3-6 6-3 7-6 (9/7) win over another American, Sam Querrey.

- PA