The second-seeded Serb lodged his disappointment with chair umpire Carlos Bernardes during the match and pointed out the issue afterward.
Djokovic says Wimbledon courts 'not that great' this year →
"I had to experience sooner or later this," he said. "I knew I could not go on playing the highest level for so many years all the time, but it's good to experience this so I can hopefully get better in the period to come."
Djokovic upset at Shanghai Masters; Murray reaches final →