The 59-year-old recounted the incident Tuesday before a jury hearing the case against Adonay Zekarias, who has pleaded not guilty to first-degree murder in the death of Semret.
Hughes testified that he used his umbrella to fend off the person who stabbed Semret in a Toronto laneway nearly three years ago.
Semret was walking home from an overnight shift at a downtown hotel on a rainy morning in October 2012 when she was attacked.
"I heard a woman screaming," said Hughes, who had been out walking in the area. "It was awful, you knew somebody was in serious trouble."
After the third scream, Hughes closed his black umbrella and began to run until he saw two figures in a laneway — a woman on the ground and a man crouched over her, court heard.
Hughes yelled to ask what was going on at which point the man stood up and turned towards him, revealing a "big knife" in his right hand, court heard.
"It's like any butcher knife, a kitchen knife, with a big silver blade," Hughes recalled. "He started jabbing it towards me."
At that point, Hughes went into what he called "defensive mode" and used his umbrella to take swings at the man wielding the knife, court heard.
"I'm staring right at his hand and just keep swinging," Hughes said. "I swung probably about three or four times by the time the knife falls out of his hand and hits the ground."
Hughes yelled at the man, telling him to get out of the area, but the man crouched on the ground and scrambled to retrieve his knife, Hughes said.
"He was making funny throaty sounds," Hughes recalled. "Like a guy in a panic."
Hughes kept swinging his umbrella, court heard, but the man managed to grab his knife, court heard.
"I take one more swing at him and my umbrella opens up. I thought I was a goner then because I can't really see nothing," Hughes said. "He's turning around and running away."
When the man fled, Hughes went over to Semret, who was moaning on the ground, and put his hand on her shoulder.
"I said, 'did he stab you?' and she said 'yes,'" Hughes recounted.
By that time, a couple from a nearby house ventured into the laneway and called 911 at Hughes's urging. But it was only once police showed up that Hughes got an idea of the extent of Semret's wounds.
"The blood was just pumping out of her back," he said.
Crown prosecutors have told the jury that Semret was stabbed seven times and died in hospital less than an hour after the attack.
They've alleged her death was a "planned and deliberate" murder.
While they don't have a motive, crown prosecutors have said Semret and Zekarias knew each other — they were both refugees from the North African country of Eritrea, belonged to the same church in their country of origin, had once lived in the same refugee shelter for a time, and went to English lessons together.
Zekarias's lawyer noted, however, that Hughes told police he thought Semret's attacker was a white man. Zekarias has light brown skin.
Under cross-examination from Zekarias's lawyer, Hughes told the court it was dark in the laneway where the attack took place and that he could only see part of the man's face because the man was wearing a baseball cap.
He also said he didn't see any blood on the hands of the man in the laneway.
Crown prosecutors have said Semret fought for her life and caused her attacker to cut himself very badly during the stabbing.
They alleged Zekarias called 911 for medical assistance for his "severe hand injuries'' hours after Semret's death, telling the 911 operator he hurt his hands lifting something.
The jury was shown photos of Zekarias' hands, taken after his arrest, that show scars on his left wrist and his right palm.
Zekarias was arrested in September 2013.