Sgt. Randy Fincham says the 25-year-old woman was waiting for a bus at 3 a.m. on Jan. 30 when she was grabbed by a man, carried onto Granville Street and sexually assaulted.
News of the arrest comes two days before Vancouver police hold a Women's Safety Fair on the campus of Langara College, in an effort to help women educate themselves on personal safety and support.
Fincham said when the woman was grabbed, she screamed loudly and actively fought back, prompting witnesses to intervene.
"It was the fact that this woman did what she needed to do to defend herself and the fact that she screamed loud enough that people could come forward and assist her and help her in scaring this person away that likely prevented her from getting more seriously injured," Fincham said at a news conference.
"This woman maintained her composure and she did what she needed to do to save herself."
She suffered injuries to her face, back and leg and was taken to hospital, where she was treated and released.
Her attacker suffered scratches to his face, Fincham said.
When witnesses intervened in the attack, police said the man bolted and tried to get into several taxis, but he was refused service and he fled down Granville Street.
"It was something beyond just a refusal of service for not wanting to give a passenger a ride home," Fincham said, declining to elaborate.
Police say they arrested 26-year-old Dustin Burwood last weekend after they obtained a photo of a person-of-interest in the sexual assault.
Police wouldn't say how they got the photo or how the Good Samaritan helped out.
Burwood was described as known to police and officers are investigating whether he can be liked to any other sexual assaults in the city.
The Women's Safety Fair is scheduled for Friday afternoon and will include information booths sponsored by personal safety experts and a police demonstration for women by tactical training officers.
"It's not a self-defence course," said Sgt. Richard Rabinovitch, with the force's sex crimes unit.
"It's more about awareness, discussion, tools that you can have to keep yourself safer in the city."