Murray broke early in the third set, but then lost the next four games in a 6-4, 5-7, 6-3 defeat.
"I mean, to get broken two consecutive times in that situation isn't good enough," he said. "I didn't make enough balls, missed easy shots—but like really easy shots.
"There were some where he was standing in the net, you know, and I just had to hit it to the other side."
The world No. 6's only explanation was "confidence."
"Because, you know, there is no other reason for missing shots like that," he said. "Basic tennis shots that I would hope to make 99 times out of 100."
Speaking not long after the match, Murray could not point to a simple solution.
"I'll need to have a think about it and have a look at what happened," he said. "But, you know, there wasn't a huge explanation for it, because the shots I was missing...it wasn't like one shot in particular."
After returning at the beginning of the season from back surgery, Murray had been satisfied with his gradual improvement from tournament to tournament—until the third set of this match.
"That's concerning for me," he emphasized. "The rest of the matches I have played since I have come back haven't been particularly concerned about them."