Attack victim Ainsley Gillespie has told her German Shepherd Jaeger chased off a man who grabbed her while she walked through Monkton Park.
Miss Gillespie, 22, was out walking her nine-year-old dog along the dark riverside footpath near the Olympiad leisure centre at 7pm on Sunday when the man approached her and asked her for a light.
When she said no he violently pulled her towards him with both hands.
But Jaeger, who had been sniffing around some bushes a few yards away, sprang into action and chased him away.
Miss Gillespie said: “I was lucky I had a dog. Someone else might not have.
“Jaeger’s a big softie when you get to know him but he is very protective.
“It was quite dark. I’d moved away from the top of the hill where the lights are, because there was a man walking a Collie and Jaeger doesn’t really get on with other dogs.
“It happened really quickly, in about 10 or 15 seconds.
“My first reaction was that he was going to attack me because he was a lot bigger than me, at least 6ft.
“He pulled me very aggressively. He didn’t say what he wanted, that was the scary thing.”
Miss Gillespie moved to Chippenham from Bolton last June and works for recruitment agency Acorn.
“It was a bit of a shock,” she said. “I thought this was a really nice place. I’ve never had any problems here before.
“I don’t know what would have happened if Jaeger hadn’t been there. He’s nine now but he’s still got a bit of life.”
She hopes a man walking his Collie can help to identify her attacker after he ran off in his direction. Police would like to hear from him.
The attacked is described as white, about 6ft tall, of slim build and in his 30s.
He had short dark hair and facial stubble and was scruffy looking. He was wearing a big, solid dark coloured, waist length duffel coat in a waterproof fabric.
Information can be sent to PC Jackie Williams 1507 or via Crimestoppers anonymously on 0800 555 111.