After Kyrgios let two serves pass him by while he was a set and 3-0 down to the Frenchman and reportedly threatened to quit the match, umpire Mohamed Lahyani climbed down from his chair and said he wanted to "help" the 23-year-old Aussie.
"I want to help you," Lahyani could be heard telling Kyrgios from TV microphones, "I know this is not you."
The pep talk had quite the effect with the world No. 30 going on to claim the set and win the match against Herbert 4-6 7-5 6-3 6-0.
However, several tennis players and commentators were quick to criticize the umpire's intervention.
"I don't think this is appropriate for an umpire," 27-year-old Herbert told reporters after the match.
"We don't know what would have happened if he (Lahyani) didn't do it. We're not supposed to have a coach on court," he said, suggesting that he could have won if the umpire didn't intervene.
"Nick from his side is not to blame as he did not ask for anything. But his behavior and motivation on court changed from this moment and then he dominated the match," Herbert said in a statement.
The Association of Tennis Professionals
rules that male players are not allowed to receive on-court coaching and Herbert said he believes Lahyani should be sanctioned for his actions.
"If he makes a mistake, I think he should be also punished.
"He doesn't make that many mistakes, I think he's a really good umpire but today I think he went over what he should have done," Herbert told reporters.
After the game, Kyrgios said the umpire's actions didn't affect his performance.
"It didn't help me at all," he told reporters. "I'm not sure it was encouragement. He said he liked me -- I don't know if that's encouragement. He was just concerned with how I was playing."
'The USTA is clearly taking us for fools'
In an earlier statement the United States Tennis Association
said Lahyani "left his chair to check on the condition" of Kyrgios.
"Lahyani was concerned that Kyrgios might need medical attention," it said.
"He also informed Kyrgios that if his seeming lack of interest in the match continued, that as the chair umpire, he would need to take action."
However, Herbert said he was "even more upset" about the USTA's statement and said the association is "clearly taking us for fools."
"We all hear on the video what the umpire said to Nick, overpassing his functions."
However as the furore grew over the incident, the USTA changed tack.
"After a comprehensive review conducted by US Open officials, including US Open Tournament Director David Brewer, Tournament Referee Brian Earley and others, the US Open determined that chair umpire Mohamed Lahyani's conduct during Thursday's second-round match involving Nick Kyrgios and Pierre-Hugues Herbert went beyond protocol," said the USTA statement.
"Lahyani was advised to adhere to proper protocols in all matches that he officiates moving forward.
"Lahyani will continue to officiate during the 2018 US Open. His performance will continue to be evaluated, as will that of all chair umpires throughout the course of the US Open."
Federer: 'A conversation can change your mindset'
Kyrgios will now face 20-time grand slam champion and world No. 2, Roger Federer on Saturday and the Swiss star also weighed in on the debate while talking with reporters on Thursday.
"It's not the umpire's role to go down from the chair," he said. "He (Kyrgios) behaves the way he behaves and then you as an umpire take decision on the chair -- do you like it, or you don't."
Federer added that it's not an umpire's role to kick players into gear.
"It's a conversation, and a conversation can change your mindset.".
Other tennis stars chimed in, including former US Open champion Andy Roddick.
"Layhani is a good man who genuinely cares about people," he tweeted. "I really like him as a human. He did something he shouldn't have. This is behavior we should see more of these days. Unfortunately it was the wrong time/place for it. Selfishly I hope they go easy on him."
World No. 41, Donna Vekic also questioned Lahyani's interaction.
"Didn't now umpires were allowed to give pep talks," she tweeted.
Kyrgios replied: "Don't be salty that you are out of the US Open," he tweeted, though the Australian subsequently deleted the tweets. "Ironic coming from someone who gets on court coaching every week of the year and also out of the US Open."
He then tweeted: "I shouldn't have tweeted so quickly after the match. Everyone is entitled to an opinion but I can assure you it wasn't coaching."
Previously Kyrgios has been handed an eight-week ban and fined $40,000
by the ATP for not giving his "best efforts" -- or in tennis terms, "tanking" at the Shanghai Masters.
He's also previously been fined for his behavior at the US Open and has collected fines in the past at Wimbledon.