Police and security guards also quickly took action to keep the Just Stop Oil protesters - the latest to demonstrate at a major sporting event in Britain this summer - from causing a bigger disruption during Friday's second round.
Merseyside Police later confirmed that four people had been arrested on suspicion of conspiracy to commit criminal damage and public nuisance.
Horschel had helped remove one protester who had tried to throw powdered orange paint on the green of the newly-created hole that's been the centre of attention at Hoylake this week.
A smoke flare was also let off but play was quick to resume soon after organisers had cleared the orange paint which caused no damage.
Horschel, who had been playing the hole at the time alongside Corey Conners and Alex Noren, had helped a greenside marshal remove one of the protesters who had been wearing white "Just Stop Oil" shirts.
Two protesters were immediately taken away from the green, while two others were later escorted away separately.
Local police said that two men and two women were detained "on suspicion of conspiracy to commit criminal damage and public nuisance."
Just Stop Oil wants the British government to stop new oil, gas and coal projects and the organisation has interrupted a host of major sports events of late, including Wimbledon, an Ashes Test and the world snooker championship.
The incident happened soon after Australian player Travis Smyth shot the first hole in one ever recorded in an Open on that same hole.
