Nick Kyrgios has admitted he spat in the direction of a "disrespectful" spectator at the end of his five-set victory over Britain's Paul Jubb.
The Australian was seen exchanging words during his thrilling 3-6 6-1 7-5 6-7 (3-7) 7-5 win on court three.
Kyrgios said he believed the fan had come to the match "just to stir up and disrespect".
Asked if he spat towards the person in the crowd, Kyrgios replied: "Of one of the people disrespecting me, yes."
The 27-year-old added: "Yes. I would not be doing that to someone who was supporting me.
"Today, as soon as I won the match, I turned to him...I've been dealing with hate and negativity for a long time, so I don't feel like I owed that person anything.
"Like, he literally came to the match to not even support anyone really, it was more just to stir up and disrespect. That's fine. But if I give it back to you, then that's just how it is."
Kyrgios could face a fine for the incident if the umpire were to the notify the referee's office who, in consultation with the Grand Slam supervisor, would decide on any punishment.
Kyrgios dropped the first set against Jubb but fought back to win the next two, before the 22-year-old Briton won four successive points to clinch the fourth on a tie-break.
In a dramatic finale, Jubb broke back to level at 5-5, but it was Kyrgios who managed to find the decisive blow on Jubb's serve to seal a battling success.
Kyrgios was also visibly frustrated with some of the line judges and spectators throughout the match and, on one occasion, asked the umpire to remove people from the crowd.
"I don't go to their nine to five and start clapping when they're scanning (items) at a supermarket, do I?" he said.
Kyrgios claimed he suffered racist abuse during his semi-final defeat by Andy Murray at the Stuttgart Open earlier this month and, while he said that was not the case at Wimbledon, he questioned the growing trend of sporting athletes who are being abused by members of the crowd.
"I love this tournament," he added. "It's got nothing to do with Wimbledon.
"I just think it's a whole generation of people on social media feeling like they have a right to comment on every single thing with negativity. It just carries on to real life.
"Because there's a fence there, and I physically can't do anything or say anything because I'll get in trouble, they just feel that they're just able to say anything they want.
"Not today, no, no (racism). But a lot of disrespect was being thrown today from the crowds. I'm just starting to think that it's normal when it's really not."