It was 4.30am on a Sunday morning last March when the 56-year-old was woken up by Philip McGilvray, 33, and Alan French, 32, shouting in the corridor outside his ground-floor room, Newcastle Crown Court heard.
Mr Mantle, who was working locally, twice asked the pair to keep quiet and was on his way to the Quayside Travelodge reception to complain when they laid into him, the jury heard.
Jolyon Perks, prosecuting, said: "As he approached the two defendants they deliberately blocked his path.
"He told them he needed to get past and placed his hands between them, and tried to force his way through, perhaps not unreasonably considering the situation he was in.
"At this point they both decided to grab his arms and set about him.
"Both men threw a flurry of drunken punches, some landed, some didn't.
"Ultimately, it ended with him being dragged on the ground face down."
French was on top of the actor and McGilvray was by his left side, Mr Perks said.
"Mr Mantle was aware that Mr McGilvray's head was close to his and it was at this point he felt a very sharp pain to his ear."
Mr Perks said the row had "culminated with a substantial part of his ear being bitten off".
There was no dispute about what McGilvray did, the court heard. French was charged with the same offence because he was jointly responsible, Mr Perks said.
McGilvray will argue self-defence, the jury heard.
The defendants, from Hamilton, Scotland, were visiting Newcastle with friends and had been out drinking.
"You may think the drink converted them to being raucous and, ultimately violent," Mr Perks said.
A nurse staying with her partner heard the fighting and came out of her room after Mr Mantle shouted: "You have bitten my ear off."
Alice Klenk grabbed both defendants by the scruff of the neck "to stop them having another go at Mr Mantle", the jury heard.
She saw the severed part of his left ear still on the carpet.
McGilvray stated he had been assaulted - not Mr Mantle, the court heard.
"The defendants' actions thereafter are telling", Mr Perks said.
"Rather than wait for the police to explain how they were the victims in this case, both of them left the scene."
They tried to get a room in a Premier Inn without success and returned to the Travelodge three hours later when they were arrested.
Later, McGilvray told detectives he bit the actor because he had been attacked.
"At the time Mr Mantle was on top of him and he couldn't get him off", Mr Perks said McGilvray told police.
"He stated he was afraid at the time and felt ashamed of his actions."
French said he played no part in the attack.
Mr Perks said: "He stated Mr Mantle had gone for his friend and his only role was to try to pull them apart."