park in Coventry with his mistress, Liz Maxted-Bluck, 49, when he heard screaming from a wooded area and ran off to investigate.
He found Esmail Adhami, 18, molesting a woman he had dragged into the underbrush.
The hound lunged at the man and chased him away. Then he circled the sobbing victim “like a guard dog” until police arrived.
Adhami was later caught and last week was sentenced to four years in prison for sexual assault.
At the sentencing in Warwick County Court last week, Judge Christopher Hodson said: “I have not the slightest doubt that if that dog had not come bounding up, worse would have happened to that lady.”
Maxted-Bluck, a professional musician, told The Express of Britain: “Jake was just incredible and probably saved the woman from being raped. He has always hated conflict, so when he heard her screaming he must have known someone was in trouble. After he ran back to the woman, I rang the police and he circled us like he was guarding us. The woman was very grateful.”
Adhami had picked out his victim last July while bicycling through the park. He dropped his bike and exposed himself to her before dragging her into the bushes.
Maxted-Bluck said: “I heard shouting and screaming and thought it was just kids, but Jake ran off into the woods.
“I went to catch up with him and the next thing I knew this bloke is running towards me with a terrified look on his face and Jake is about two feet behind him. When I caught up with the girl it was strange. It was like Jake knew what had happened.”
Police caught Adhami hours later and discovered he was in the county illegally after a failed asylum application.
The court heard that weeks before the attack Adhami had been arrested after sexually assaulting a 13-year-old girl but was released on bail.
Adhami was also placed on the sex offenders register for life, banned from having contact with girls under 16 and told he was likely to be deported upon his release from prison.