Police arrested two protesters for trying to disrupt the Epsom Derby, including one who stormed the track after the race had started on Saturday afternoon.
A man was tackled to the ground and handcuffed by officers after scaling barriers and running on to the racecourse.
Revellers booed and shouted "get off!" as he was chased by stewards before being swiftly removed from the path of the horses.
Minutes later, a woman attempted to climb the fence but was pulled to the floor by police. Footage posted on social media showed the protester sitting on the ground as officers handcuffed her before carting her off.
Animal rights' group Animal Rising confirmed the man was one of its supporters.
Despite pledges by the activist group to “cancel or severely delay” the Derby, the race continued as planned shortly after the protesters were carried away.
Animal Rising accused the Jockey Club, owner of Epsom Downs racecourse, of endangering the lives of animals.
"Despite The Jockey Club's claim that the horses safety is paramount, they decided to start the race despite knowing that a protester was on the tracks," the activist group tweeted. "Another sickening display of profit [over] care for animals."
Observers described the protest as “ludicrous” and “absolute insanity” while others thanked police for putting a stop to the planned disruption.
Earlier, Surrey Police said they had arrested 19 people in a bid to thwart Animal Rising's plan to prevent one of England's biggest horse races from going ahead.
The campaign group accused the force of abusing their powers and using “intimidation tactics”, but vowed members would push ahead with efforts to stop the Epsom Derby.
Hours before the race, officers swooped on two properties in Mitcham and Byfleet and detained 11 people after warrants were obtained “based on intelligence”. A further eight people were arrested after their vehicle was stopped near the racecourse.
All 19 people were arrested “on suspicion of conspiracy to commit public nuisance and remain in police custody”, the force said.
Animal Rising had publicly announced its plan to disrupt the Derby as tens of thousands of racing fans flocked to the town.
“We have been clear in our approach that criminal activity will not be tolerated at the Epsom Derby Festival,” said Superintendent Michael Hodder of Surrey Police.
“As a result of intelligence, we have arrested 19 people who we believe were intent on illegally disrupting today’s events.
“Our officers will be at the event throughout the day to continue in keeping the public safe and preventing criminality.”
In an announcement following the initial arrests, Animal Rising said police would not prevent them from pushing ahead with their planned action to disrupt the race.
“Earlier this morning, at least 10 arrests were made by Surrey Police, allegedly in connection with the Epsom Derby,” the group said.
“This comes after reports of facial recognition cameras around Epsom Downs Racecourse.
“Police heavy-handedness and intimidation tactics will not prevent a national conversation about our animals and the natural world.
“It restates its commitment to protect horses and disrupt the Derby.”
In April, Animal Rising's members stormed the racetrack ahead of the Aintree Grand National and caused the race to be delayed.
Ahead of the Epsom Festival, the group pledged to continue its campaign of “peacefully disrupting” major fixtures in the horse racing calendar.
A spokesman for the group said demonstrators would attempt to shut down the Epsom Derby in a bid to protect the horses.
The Jockey Club was last week granted a High Court injunction against Animal Rising, claiming it had made “explicitly clear” it intended to breach security at the racecourse.
Writing on Twitter, the activist group claimed members were willing to “put their bodies on the line”.
Speaking ahead of the planned protest on Saturday, Animal Rising's Nathan McGovern said: “We are looking to continue the conversation that we started at the Grand National about our broken relationship with animals and nature.
“On the ground we are looking to cause the cancellation or severe delay of the event so that everyone in the country has this discussion.”
Animal Rising tweeted: “We will be peacefully disrupting the tracks of the Epsom Derby this weekend. And we will be holding a peaceful alternative festival outside the front, with no animals being harmed.”
Earlier, a spokesman for Surrey Police said that, while the force would help support peaceful protests, they would “not tolerate” criminal activity or risks to the public.
“The guiding principles of policing protests are the safety of protesters, the public and police officers involved, preventing criminal behaviour or disorder and de-escalating tensions,” the spokesman said.
“We do not comment on officer numbers for operational reasons, but our officers are well-trained in responding to protests and will be on hand throughout the day to police the event.
“Where lawful, we will seek to facilitate peaceful protests.
“Any criminal activity or risk to public safety will not be tolerated, and we will take robust action in response to this.”
The injunction granted by High Court judge bans people from going on to the racetrack and carrying out other acts with the intention or effect of disrupting the races.
Such acts include intentionally causing objects to enter the racetrack, entering the parade ring, entering or remaining on the horses’ route to the parade ring and to the racetrack without authorisation and intentionally endangering any person at Epsom Downs racecourse during the two-day Derby Festival.
Anyone in breach of the court order may be subject to contempt of court proceedings and fined or jailed.
Claudia Penna Rojas, of Animal Rising, said she would “do right” by the horses, even if it meant breaking the law.
“If it means breaking the law, we know that law isn’t always equal to morality and we know that people have had to break laws throughout history to create the change that we need,” she told Sky News earlier this week.
In April, the Grand National was delayed by just over 10 minutes after demonstrators ran on to the track in a bid to stop the race.
Several protesters were arrested in the incident which sparked a public debate about the sport.