John McFarlane was repeatedly struck with a bottle as he walked alone in Glasgow's Dennistoun last December.
The 35 year-old required surgery after the assault.
His attacker Gary Strachan was caught on CCTV and is now behind bars after he pled guilty to assaulting his victim to the danger of his life.
The 27 year-old will learn his fate when he returns to the High Court, in Glasgow, next month.
Mr McFarlane was set upon as he headed home from celebrating his birthday in the early hours of December 1.
CCTV footage played in court showed Strachan out at the same time with a friend who was walking a dog in the city's Meadowpark Street.
Strachan was then suddenly seen running across to Mr McFarlane and lashing out with a Buckfast bottle.
The thug's friend eventually pulled him away before the blood-soaked victim tried to get help.
Judge Lord Turnbull remanded Strachan in custody and deferred sentencing for reports.