Ricky Morgan, 34, almost severed the finger of James Porritt, cut his wrist down to the bone, and left him with a deep wound to the left side of his head as well as a cut on his leg.
At least 30 passengers stampeded into an adjacent carriage on the Jubilee Line train as the attack unfolded, screaming and falling over each other in a bid to get away from Morgan, the court heard.
Jurors were told the attacker “let out an unholy scream” as he mounted the attack, which he insisted was “not a terrorist attack” and only directed at Mr Porritt.
After his arrest at Green Park station, Morgan told police: “If I had known it would cause this much drama, I wouldn’t have done it”.
He admits carrying out the stabbing, but denies attempted murder on the grounds of insanity.
Prosecutor Grace Ong said the victim, Mr Porritt, had been to the gym and was on his way to meet his girlfriend and her father when he was randomly attacked, at around 6.30pm on July 9 last year.
He had made the fateful decision to take the Jubilee Line due to delays on another line, coming across Morgan who was carrying a machete and lock knife in his bag.
Describing the attack to police, Mr Porritt said: “I was pleading, please stop, please stop.
“I was in shock, it was like a horror movie. I genuinely thought he was going to kill me.”
He said it was “so surreal” to be targeted by a stranger on a rush hour train.
“He just would not stop. He was relentless. He said he did not want anybody else, he just wanted me. He was fixated with me,” Mr Porritt said.
“James Porritt and Ricky Morgan were complete strangers”, said Ms Ong. “This was a completely unprovoked attack upon a commuter on the Jubilee Line going about his daily business.”
Mr Porritt told police he noticed Morgan in the carriage, and he then “heard screaming” while he was looking at his mobile phone.
“The next thing he knew was that the defendant was hitting him over the head with an object”, said the prosecutor.
“He put up a hand to his head to protect himself and his hand was hit as well. He showed the police his right hand which was in pieces. He could see through to the white of the bone in his fingers, there was blood coming from his head, hands, and elbow.
“At one point, Mr Porritt lifted his leg to protect himself further and this was struck as well.
“Almost impossibly, he managed to finally get himself away from his attacker, holding separated parts of his hand together. He managed to get through the carriage door.”
Ms Ong said Morgan “appeared to be fixated on Mr Porritt”, and was heard shouting at him: “I don’t want anyone else, I just want you.”
A woman, who was on her way to a concert with her sister and a friend, reported seeing Morgan “holding the machete above his head and bringing it down with all his force”.
She and her sister, whose leg was covered in Mr Porritt’s blood, fell to the floor with other passengers in the scramble to escape, and they became seperated from their friend – fearing she too had been stabbed.
The friend told police she heard the attacker shouting: “This is not a terrorist attack.”
Another passenger described a “look of anger flash across his face”, the court heard, while a man on board with an eight-month-old baby said: “Suddenly 30 to 50 people were running down. At the back of the group was James Porritt, blood coming from his head and his leg had been chopped.
“Mr Morgan was walking towards them, he had a machete in his right hand with blood on it, and a knife with a six inch blade. He said they started it, I’m not coming for you, it’s them.”
A doctor on board the train gave first aid to Mr Porritt, as police intervened to stop the attack and arrest Morgan.
Jurors heard Morgan, of no fixed address, is pleading not guilty to the attempted murder charge on the grounds of insanity.
The trial continues.