The two fugitives bucked their riders on the beach near Lancing at around 6pm and made off west along the seafront.
Worthing's Lindsey Pearce was passing the horses in her car next to Brooklands Park, when she said she saw them galloping across the beach and clearly out of control.
After gaining experience among horses from her childhood, she turned the car around and gave chase, driving behind the galloping horses with her hazard lights on.
"I followed them and they were going onto the path, coming up behind cyclists and warlkers who had no idea they were there," said Lindsey, who was accompanied by taxi driver Trevor Goss who followed behind.
"I was just waiting for someone to be smashed by those horses, but I couldn't beep my horn to warn them or I would frighten the horses even more."
Lindsey briefly lost the horses as they headed up the pedestrianised Warwick Street so, aided by her six-year-old son who was in the car, she drove parallel and followed the crowds of shocked pedestrians until she picked up the trail again in Shelley Road.
The whole time she was updating the police on hands-free, she said.
From Shelley Road, the pair made their way along Heene Road and eventually onto Tarring Road, where they drifted towards the level crossing in another heart-in-mouth moment.
Luckily the tiring mounts took refuge in the car park of West Worthing Social Club in Elm Grove, allowing Lindsey and Trevor - who had been following since Brooklands Park - to block the entrance and hem them in.
They managed to calm the horses down and walk them around until they relaxed and police arrived around five minutes later.
Shortly after the distraught owners arrived, having been left in the wake of their only modes of transport.
Lindsey said one of the horses appeared to have been clipped by a car, but both were relatively unscathed in a situation that could have been much worse at several points during the 20-minute pursuit.
"I was just waiting for it all to go horribly wrong, I knew how much damage they could cause," she said.
"I found it really stressful only being to follow and watch, but my son found it very exciting, shouting to me when he saw them after we'd lost them.
"It could certainly have turned out a lot worse."
With no trailer to hand, the horses were led back through town by their relieved owners. See pictures of the drama here: Worthing’s wild horses: Pictures show riders thrown from their mounts and rescue effort