A man's ear was almost severed when a neighbour battered him with a broken bottle.
Police arrived at the Hamilton address to find a bloodbath, the town's sheriff court heard on Friday.
Kevin Kelly, 33, of Kelvin Gardens, admitted assaulting Raymond Sullivan to his severe injury and permanent disfigurement at the victim's home in the same street on May 5.
Co-accused John Cairney, 31, a prisoner, had his not-guilty plea to the charge accepted.
Mr Sullivan suffered wounds to his head, neck and body requiring 15 stitches.
Doctors at the Queen Elizabeth hospital in Glasgow found that his left ear was partially severed.
The court heard that Mr Sullivan, his girlfriend, Kelly and Cairney had been taking alcohol and heroin.
At one point Mr Sullivan and his partner started arguing and the other men became involved.
Lauren Cole, prosecuting, said: "The situation escalated and Kelly hit Mr Sullivan over the head with a glass bottle.
"The bottle smashed and he continued to strike him on the head, neck and body with the broken glass.
"When police arrived Mr Sullivan's partner stated, 'Kev battered Sully because Sully was being cheeky to me'.
"She was wearing a pink hoodie that was covered in blood. Mr Sullivan himself was covered in blood as was a bedroom, with broken glass on the floor."
Defence agent Tony Linden said Cairney went to the woman's aid after Mr Sullivan assaulted her.
The solicitor stated: "Kelly formed the view that Cairney was very much on the receiving end from Mr Sullivan and made the mistake of becoming involved.
"But what he did was entirely disproportionate and excessive.
"I appreciate his record is unimpressive. For many years his life has been blighted by drugs and alcohol."
Sheriff John Hamilton said it was a "nasty" assault and noted that Kelly had been imprisoned for assault on two previous occasions.
The sheriff jailed him for 18 months but backdated the sentence to May 9 as he had been in custody since then, awaiting the court case.
That meant Kelly was likely to be freed immediately under early release rules.
*Don't miss the latest headlines from around Lanarkshire. Sign up t o our newsletters here.
And did you know Lanarkshire Live had its own app? Download yours for free here.
