The Aussie appeared to be offering minimal effort on the Herbert serve, something he has been accused of in the past and his actions have consistently left fans, umpires and opponents flummoxed.
However, the match sparked a huge row after respected umpire Mohamed Lahyani lost patience with the under-performing 30th seed and climbed down from his chair to tell the Australian to try harder.
"I want to help you", Lahyani could be heard saying.
Kyrgios went on to see the trainer a couple of games later before breaking back to overturn the deficit and then run away with the contest in the third and fourth sets.
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But when the trainer arrived and asked what Kyrgios needed treatment for, the Australian said: "I don't know, check my wrist or something".
Later on Thursday, the U.S. Open put out a statement, explaining the interaction between Lahyani and Kyrgios.
Following his match with Mischa Zverev at the 2016 Shanghai Masters, Kyrgios was fined and banned for eight weeks for "lack of best efforts".
Federer's blast came too late to save a fuming Herbert, who was cruising to a huge upset win when Layhani's intervention changed the momentum. "'Oh, I'm not feeling so well.' Go back up to the chair", he said.
"I am racking my brain to think of a situation requiring a chair umpire to speak like that to one player".
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Croatia player Donna Vekic added: "Didn't know umpires were allowed to give pep talks". I just saw that Nick from that point started to play really focused, 100%. "You are great for tennis". "I can't think of one", Ings tweeted.
Kyrgios has been forced to undergo work with sports psychologists in the past by the ATP in light of him openly tanking matches, and there had been occasions in this match before the pep talk when he was not even moving to return serves. It's not the umpire's role to go down from the chair.
"I want to help you".
"Lahyani was concerned that Kyrgios might need medical attention".
The Frenchman said: "On court I tried to focus on myself". I didn't listen to what they said.
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