David Brandwood, 38, of Canal Walk, Chorley, pleaded guilty to wounding NHS worker Victoria Wright on the basis he had swept the glass from her hand intending to spill the contents in her face, but had not intended to strike her with it.
He forcefully knocked the glass from her hand as his girlfriend was pulled out of the club by the bouncers after striking her friend.
The woman, who suffered a severed facial artery, was left with permanent scars and lost a tooth following the incident at the Lost Bar in Chorley on February 9, 2020.
Brandwood's girlfriend was later given a caution.
Prosecuting, Paul Brookwell said earlier in the evening Miss Wright had been out with her friends and there had been an argument between Brandwood's girlfriend and her friend.
He said: " Then, as fate would have it, this complainant moves to a different bar, The Lost Bar, and the defendant and his partner were also in that club.
"Apparently the defendant's girlfriend approached the complainant's friend and there was a blow struck.
"The bouncers came in to remove her.
"You can see it's one action, with some degree of power - he swings his hand across and the glass then carries on and goes into her face causing the injuries.
"There is no question of a premeditated arming with any weapon, but it's clear the glass smashed and caused very severe cuts and injuries.
"There's no suggestion it was deliberately rammed into her face it was a sweeping action."
The defendant was arrested that night and accepted he had caused the injuries.
In a statement the woman said the scars were a "permanent reminder of what that man has done to me" and said she had become very nervous and had to have counselling.
Defending, Chris Hudson, said Brandwood was distraught when he learned in an interview what he had done, and would lose his job and home if he went to jail.
He said: " He felt it was unfair his partner was being excluded and also felt there was a degree of crowing on behalf of the complainant."
Judge Beverly Lunt told Brandwood there was no possible justification for the attack and that an immediate prison term was the only appropriate punishment.
She said: "Whatever may have happened earlier in the evening, once you were in this particular venue the only person who appears to have behaved lawfully is the victim of your assault.
"She did a sarcastic wave but that is all - and you deliberately then turned and grabbed the glass you saw she was holding in order to throw her drink.
"You lost your temper and you lost control."
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