An announcement was made over the stadium PA in the second half, saying: "Racist behaviour among spectators is interfering with the game." It was the first time FIFA's protocol for dealing with discrimination at football games was implemented in England's top division. Two further announcements, timed at 10-minute intervals, followed.
The visitors had opened the scoring on 12 minutes as Willian curled a shot past Paulo Gazzaniga from near the edge of the Tottenham box, and they doubled their lead on half-time when Willian struck again, slamming home a penalty.
The spot kick was awarded following a VAR check after Gazzaniga rushed out of goal and collided with Marcos Alonso.
There was another VAR check in the second half after Son Heung-Min kicked out at Rudiger, resulting in the South Korea international receiving a red card.
Crowd trouble immediately followed as an item was thrown at Chelsea goalkeeper Kepa Arrizabalaga before the first announcement about the reported racist abuse was made.
Chelsea captain Cesar Azpilicueta said Rudiger complained to him about hearing monkey chants.
Speaking after the match, he told ESPN: "The situation is clear. Toni came to me and he informed me [of the abuse]. We have had many meetings with the Premier League and also with the referees before each game [about this]. We are trying to fight racism, at Chelsea especially we have many campaigns against it.
"In the moment that happened [today] I went to the referee and I told him. Right now it is under investigation and hopefully such incidents don't happen again. We have to work hard to end racism."
A Tottenham spokesperson told ESPN that, despite the anti-racism protocol stating a match should be suspended after three stadium announcements, all three in this case were in relation to the same incident, meaning the correct process was used.
"All I know is Toni Rudiger heard racist chanting or comments. I haven't had an individual conversation with him, I've only addressed the group," said Chelsea boss Frank Lampard after the match. "I will support Toni as I would with any of our players -- in fact, any opposition players -- when this happens, whatever stadium it happens at, it needs to be dealt with.
"As I don't know any more than that, we'll wait for the process to happen."
Lampard added: "If it is a fact, true and it happened then it needs to be dealt with, and the punishment needs to be strong."
Tottenham released a statement Sunday afternoon, saying: "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."
The alleged racist incident is the latest one at a high-level Premier League game. Manchester United's Fred claimed he was victim of a monkey gesture by a Manchester City fan.
In July Chelsea banned one of their fans for life after he racially abused Manchester City's Raheem Sterling.
Tottenham defender Toby Alderweireld said players were "sick of it" when asked about the incident while Tottenham manager Jose Mourinho said "every club was together" in the battle to eradicate racist behaviour from the stands.
"I was losing, I didn't want the game stopped but immediately when I knew the reason why it was stopped I obviously understood and accepted it," Mourinho said.
"The club is also a very proud club in this kind of situation and the club also internally will try to delete it.
"I'm disappointed that things like that still can happen, but the referee stopped the game. He spoke to the players, he spoke to the captains, he spoke with the coaches."
Sunday's game marked Lampard and Mourinho's second time facing off as managers, with the former's Derby team knocking Manchester United out of the Carabao Cup in 2018. Lampard played under Mourinho for the entirety of the latter's first tenure as Chelsea boss between 2004 and 2007, and for one season after the Portuguese's return to Stamford Bridge in 2013.
The result -- Lampard's first win over a so-called top-six side as Chelsea manager -- sees the Blues remain within six points of third-placed Manchester City and four ahead of fifth-placed Sheffield United.
Meanwhile, Tottenham sit in seventh place, six points off of the Champions League positions and one point in front of Manchester United, who suffered a 2-0 away loss to bottom-placed Watford earlier on Sunday.
Information from Reuters was used in this report.