William Patterson brutally attacked Alexander Montgomery at his flat in Clydebank last March.
The pair had been on a night-out at a nearby bar before Mr Montgomery was subjected to an apparently unprovoked assault.
Patterson, 30, admitted an attempted murder charge when he appeared at the High Court in Glasgow.
A judge remanded him in custody and deferred sentencing until March for reports.
The two men - along with Patterson's brother Stephen - had been at a local bar last March 25 when they went back to Mr Montgomery's home in Montrose Street, Clydebank.
The court heard that later the night Patterson struck Mr Montgomery with a beer bottle.
Prosecutor Adrian Cottam said the 30-year-old victim passed out and had no memory of what happened next.
Mr Cottam told how Patterson, of Craighaw Street, Faifley, punched Mr Montgomery and struck him in the neck with a knife.
Lord Turnbull said: "It is surprising indeed that Mr Montgomery did not die."