The Scot went down 6-3, 6-2, 6-1 in an hour and 40 minutes of brutal hitting, with his legs simply unable to do the work needed to keep up with the world No.1.
The seventh seed had required four and a half hours longer on court than Nadal to reach the last four in Paris and Murray admitted that may have been a factor.
"If it was, I've only got myself to blame because I was in control of a lot of the matches that went longer than maybe they should have," he said. "If that did have anything to do with it, it was completely my fault.
"There were a few too many sets this week in matches where I was up. I could have finished sets quicker, could have finished matches quicker. That's something during the grass [court season] and over the next few months that I'll definitely need to work on - not letting guys back in when I've got the match won. That's something that Rafa has obviously done incredibly well, especially here."
Murray began the match looking to be aggressive but, with his body not up to the task, he made mistakes and Nadal took control. The Spaniard said he played "my best clay-court match this year" and will meet Novak Djokovic in the final, a match that will also decide who has the world No.1 ranking going into Wimbledon.
Having equalled his best result in reaching the semi-finals in Paris, Murray was desperately disappointed not to have performed better, especially after pushing Nadal so close in Rome earlier this month.
"I knew it was going to be a difficult afternoon before I went on the court," Murray said. "It was a tough day for me. It was a bad, bad day. I'll need to bounce back quickly from it."
The Scot will now head to London and Queen's Club to begin the defence of his Aegon Championship title on Monday.