The millionaire duo, along with Noiseworks frontman Jon Stevens, arrived at the restaurant at 1pm on Monday, with the fight not breaking out until three hours later.
Mr Singleton, who cashed in his majority stake in 2GB radio station by selling it Fairfax Media in a $200 million deal earlier this year, left the swanky steakhouse shortly afterwards and was carried across the road by Stevens and another man to the nearby Bells Hotel.
A noticeably intoxicated Mr Singleton claimed his 'lapse in class was not appreciated by Cowin', according to The Daily Telegraph.
"Singleton was displeased with this and whacked Cowin over the head with a bottle," Mr Singleton said, speaking in the third-person.
"Singleton grabbed the next glass from the floor and slashed Cowin's ear."
An eye witness to the dispute reportedly told the Sydney Morning Herald: "Singo really lost it, I think everyone was pretty shocked by what they saw."
Soon after the bust up The Daily Telegraph paid about $10,000 for dramatic photographs of the fight, the Sydney Morning Herald claims.
Mr Cowin and Mr Singleton first met shortly after the former arrived in Australia from Canada in 1969.
Mr Singleton, an advertising entrepreneur in the 70s and 80s, is believed to be worth $370 million.
The father of seven from six different marriages not only has investments in the Macquarie Radio Network, which recently merged in a $200 million deal with Fairfax Media's radio division, but is also a major investor in hotels, horse-racing and publishing.
Mr Cowin is worth an estimated $940 million, according to Forbes Magazine. He is a Fairfax Media director, and a majority shareholder in Competitive Foods Australia, which runs the Australian Australian Hungry Jack's franchise.
His family owned company owns 50 KFC outlets in Western Australia and the Northern Territory, as well as 350 Hungry Jack's outlets throughout Australia.
NSW Police said a complaint had not been made by either party.
- Daily Mail