The Serb on Friday fell to his first defeat of the season in a high-quality contest lasting more than two-and-a-half hours, Xinhua news agency reported.
“What happened? I lost the match. That’s it,” Djokovic said in his post-match press conference.
It is the second time Bautista Agut has beaten Djokovic in his career and both victories occurred in a semifinal.
The first came in October 2016 in Shanghai. Djokovic was also world number 1 at that stage.
The Serb played two matches each day for three days in singles and doubles, prior to Friday’s defeat.
Including the meeting with Bautista Agut, Djokovic spent almost 10 hours on court in three days and played 11 sets in singles’ matches.
“Obviously, I’m not pleased that I lost the match today, but I lost to a better player in the end,” said Djokovic.