Novak Djokovic blamed his intense schedule on the ATP Tour for his defeat to Roberto Bautista Agut at the Shanghai Masters on Saturday.
The world number one has been out of sorts in China this week and needed to come from a set and a break down to beat Mischa Zverev in the last eight.
There was no way back in the semis, though, as Bautista Agut recorded his first win in six meetings with Djokovic – a 6-4 6-4 win setting up a meeting with Andy Murray on Sunday.
Djokovic's frustration was clearly visible as he slipped to the shock defeat, the Serbian smashing his racket, ripping his shirt and sarcastically applauding umpire Carlos Bernardes.
Speaking after the defeat the 29-year-old admitted the tour calendar was beginning to take its toll, but vowed to put things right.
"In terms of results it was up and down, but there are definitely things that I need to regain from the emotional, mental point of view," he said.
"So I guess I'm focusing on that more. It's a transition somewhere in between, maybe just exhausted by the amount of matches I have had in the last 15 to 20 months.
"Maybe all in all that's the cause of me feeling this way. But I had to experience this sooner or later. I knew I could not go on playing at the highest level for so many years all the time.
"I guess this is one of those days. You know, things go in an opposite direction than you want them, but again, it's a lesson.
"Every day is a lesson. You learn from these kind of days and matches more than when you're winning."