British Andy Murray won 6-4 6-2 on the clay to breeze past Gilles Simon in straight sets and will continue the defence of his crown against either David Ferrer or Tomas Berdych.
Djokovic’s reward for his 30th win of the season is a meeting with Milos Raonic or Jo-Wilfried Tsonga on Friday.
14-times Grand Slam winner Rafael Nadal was a 6-4 6-2 winner over Sam Querrey. He has won 12 straight matches at the start of the European season on clay and will meet Joao Sousa in the last eight.
As part of a five-game winning run, Murray broke Simon for the first time to clinch the first set and never looked in danger of losing.
The 27-year-old was not broken during the match as he completed victory in just under an hour and 40 minutes.
“It’s always difficult to get the balance right against him because the better you hit the ball, the faster it comes back against him,” said Murray.
“He uses the pace very well so I knew I needed to be patient and use variety, but also when the chance is there, go for it.
Sometimes he makes players rush, but today I didn’t have that problem. It was good from start to finish.
It avenges the defeat in Rotterdam last year when the Frenchman won in their only meeting on the ATP Tour.