By Mark Meadows
Simon twisted his ankle at the start of the second set and had heavy strapping applied before gingerly carrying on.
Murray showed no mercy and after the first drop had a struggling Simon stranded, the Briton regularly used his favorite shot with the boos for the world number four and cheers for Simon intensifying after each attempt.
"I thought it was a good match until he got hurt," Murray, who just a day ago was saying how the Monte Carlo Country Club was one of the best venues in the world, told Sky Sports.
"It changed the match. You always feel you are in the driving seat but it's not a lot of fun... it spoils the concentration.
"You know you are in the driving seat and you want to put the foot down and finish the match as efficiently as possible. Drop shots were winning me virtually every single point -- I had to keep moving him."
The 23-year-old, whose public image in the past suffered from occasional teenage strops, could face more grief from the crowd when he plays Frederico Gil in the quarter-finals on Friday after the Portuguese beat another Frenchman Gael Monfils.
"I don't know a lot about him (Gil) but I watched his game," Murray added. "He did well in Estoril and can play well on clay, he's proved that by getting to the quarters here this week. I'll have to be on my game tomorrow."
(Editing by Martyn Herman and Ken Ferris)