Chelsea defender Antonio Rudiger reported he was racially abused by Tottenham fans during Sunday's 2-0 win, resulting in the Premier League's anti-discrimination protocol being used for the first time.
The Germany defender was seen mimicking a monkey gesture as he and captain Cesar Azpilicueta reported the abuse to referee Anthony Taylor, before a total of three announcements were made at the Tottenham Hotspur Stadium.
"Racist behaviour among spectators is interfering with the game. Please remember that racism has no place in football," was the message over the tannoy, and Spurs immediately launched an investigation at full-time.
The incident took place around the 63rd minute, straight after Rudiger had been involved in the controversial sending-off of Spurs forward Heung-Min Son following a VAR review.
Son was shown a straight red card for violent conduct after appearing to kick out at Rudiger after he had been felled inside the Chelsea half, with the home side already trailing 2-0.
Tottenham said: "We are now conducting a thorough investigation which will include liaising with Chelsea and their players for their observations.
"Any form of racism is completely unacceptable and will not be tolerated in our stadium. We take any such allegations extremely seriously and shall take the strongest possible action against any individual found to be behaving in such a way, including stadium bans."
Rudiger: It's important to talk about racism
Rudiger took to social media hours after the final whistle to thank fans for their support over the incident, and appealed to witnesses as he hopes the offenders will be identified and punished.
"It is really sad to see racism again at a football match, but I think it's very important to talk about it in public. If not, it will be forgotten again in a couple of days (as always)," he said on his Twitter account.
"I don't want to involve Tottenham as an entire club into this situation as I know that just a couple of idiots were the offenders. I got a lot of supportive messages on social media from Spurs fans as well in the last hours - thank you a lot for this.
"I really hope that the offenders will be found and punished soon, and in such a modern football ground like the Tottenham Hotspur Stadium with dozens of TV and security cameras, it must be possible to find and subsequently punish them.
"If not, then there must have been witnesses in the stadium who saw and heard the incident. It's just such a shame that racism still exists in 2019. When will this nonsense stop?"
Azpilicueta: I reported Rudiger abuse to ref
Chelsea captain Azpilicueta explained after the game how he reported the abuse directed at Rudiger to the match referee.
"You know it is very clear every time we have meetings with the Premier League and the referees. Before the game, we have been told to report if any incidents of racism happen straight away to the referee," he told Sky Sports.
"Antonio came to me and told me that he had listened to racist songs towards him so I just reported it to the referee immediately.
"I left it to the ref to do his job. We are very concerned and aware of this behaviour, altogether we have to stop it.
"[I don't know if other players heard] because we went straight to play and then the incident with Son and his red card was towards this area, where it happened.
"I hope everything becomes clear and we eradicate it as soon as possible. It's an issue in not only football but life - we need to work together towards eradication."
Mourinho: I saw ref follow protocol
Spurs boss Jose Mourinho expressed little knowledge of the racism incident, and insisted referee Taylor and his colleagues followed the set protocol for such situations.
"I saw nothing," he said. "I saw the referee following the protocol, I saw the referee speaking with (fourth official Andre) Marriner, I saw the referee coming to me and to Lampard and tell us what was going on, and the protocol was followed.
"Every club is together on this situation and of course we are disappointed."
Lampard: I would support player walk-off
Chelsea boss Lampard lamented the situation, admitting he would support his players walking off if subjected to a future racism storm.
"In terms of walking off the pitch, I think that has to feel right in the moment," Lampard said after the game.
"And until that moment comes I don't want to guess what I would do. It would depend what the players were feeling and saying.
"But I would be absolutely, 100 per cent behind them if [they wanted to walk off], and I'm sure it would be a group decision. But we're not there yet, so it's hypothetical to a degree.
"Of course I'll support Toni as we would support any of our players, or in fact any opposition players. Wherever this happens it needs to be dealt with.
"If it happened and it's fact, then punishment is needed and it needs to be strong."
Ashley Cole: I suffered 'a lot of abuse'
Former England and Chelsea defender Ashley Cole admitted he had "a lot of abuse" from the stands during his time as a player, but never reported incidents because he did not feel he had enough support.
"You try to block it out, but obviously he (Rudiger) has heard something," Cole said on Sky Sports' Super Sunday.
"Players keep going to the referee, but we see the same things happening.
"These people need educating. In society it is easy to say what you want on social media, you don't see their faces.
"People around them need to be grassing them up, getting them thrown out and banned."
Cole added: "No one knows the answer. I don't understand how you stop it, to be honest.
"Clubs feel like they have to make announcements, but why are they waiting until something happens?
"I praise Raheem for coming out and speaking out and standing up, because I could not do it. I felt like no one cares, no one is going to listen.
"It is my fault as well for not coming out - I felt like I did not have enough support. Raheem has got the people onside, I did not think I had that."
Townsend: Need to eliminate racism disease
Kick It Out head of development Troy Townsend insists more needs to be done to tackle racism, otherwise it will continue to "fester and flourish throughout the football industry".
He also feels there needs to be more clarity on the protocol that should be carried out if a racist incident occurs in England.
Townsend said: "I'm not going to talk about anything to do with the international protocol, but we've got to talk about the protocol here and now that we're trying to administer in our English football.
"I still wasn't clear with what was going on today because there were three stadium announcements - did that mean three separate incidents or not?
"Now we understand that it was just the one incident but the stadium announcement was three times. There needs to be clarity on what are the steps anyway - are we following the same protocol as UEFA or have we introduced our own protocol that maybe not everyone is clear about?
"Protocol is one thing, sanctioning is another, actions is more important and really trying to eliminate this disease that continues to fester and flourish throughout the football industry. We really have got to tackle it head-on now."