Fatah, 67, said even the police sided with the crowd of some 100 frenzied mainly young crowd until a Deputy Commissioner of Police reached the scene and apologized.
Fatah, a liberal who is also the founder of the Muslim Canadian Congress, said he had gone on Sunday to Jashn-e-Rekhta at Janpath as a visitor when he suddenly came under attack.
"I am happy as a 67-year-old I was able to confront 20-year-old Urdu jihadists. Hundred howling hyenas let loose on me," he tweeted.
He said the crowds dubbed him a "kutta" (dog) of Prime Minister and kept screaming "Death to Tarek Fatah". All the while, although he was ringed by a hostile mob, Fatah refused to leave.
Fatah said he was kicked and attacked from behind by the crowd.
The Canadian alleged that instead of protecting him, the police "manhandled me, claiming I was the reason why the crowd was upset and that I should leave the premises".
He said when the policemen tried to drag him away, he stood his ground and sat on a chair for some two hours until a senior officer came and apologized for his colleagues' conduct.
Organisers responsible
Fatah accused the organisers of abandoning him and said he suspected it were they who sent the mob after him.
A spokesman for the organisers told IANS: "Ours is an apolitical event. We have a small team and the volunteers were busy organising the lined-up events. When we saw that it was turning ugly we decided to call the police to provide him (Fatah) security."