Anna Westby says the suspect, who has links to the Los Angeles area, approached her and three others asking for a photo, before he pulled out a knife.
She says before she could even react the man launched into the stabbing attack, which left two people dead and six others wounded.
"And he stabbed Maris in the heart," she recalled sobbing. "And Victoria ran, and he chased Victoria, and he stabbed her in the back."
Las Vegas stabbing suspect said he 'let the anger out'
Las Vegas stabbing suspect previously lived in LA, report shows
Despite being stabbed in the back herself, Westby tried to save one of her friends by putting pressure on her wound.
Meanwhile, the suspect, Yoni Barrios, is due back in court on Tuesday where he will face two counts of murder.
Barrios has a Los Angeles address.
According to the arrest report, he told officers he got angry after some of the victims laughed at him.
The two people who died in the attack have been identified as Las Vegas residents Brent Allan Hallett, 47, and Maris Mareen DiGiovanni, 30.
Las Vegas stabbing suspect ID'd after 2 killed, 6 wounded with kitchen knife in attacks along Strip