The world No.1, who has now won 32 sets in a row on clay, inflicted a heavy and damaging defeat on a possible Roland Garros title contender.
It was another top-notch display from the defending champion, however his dispirited opponent performed well below his optimum level.
The Austrian’s game crumbled as his ruthless rival flexed his muscles, and he endured a torrid 68 minutes.
Thiem is widely considered to be the second best clay-courter around, yet he struggled to just win games against the Spanish juggernaut.
The loudest cheer of the afternoon was saved for when the Austrian finally got his side of the scoreboard moving in the second set – and the sympathy of the crowd further highlighted the one-sided nature of this eagerly anticipated match-up.
Grigor Dimitrov will attempt to become just the fourth player to defeat the ‘King of Clay’ on the Cote d'Azur. The Bulgarian, a local resident, defeated David Goffin 6-4 7-6(5) to reach the semi-finals.
“I felt I did a lot of things better than the previous days,” said Dimitrov. “I started the match better and I served better, but then, at the same time, it's a clay-court and anything can happen in a way.
“You always want to have that fight and that excitement to kind of come through it, but it's very taxing physically. There were a lot of positives from today's match. That's all I can say.”