The 'Braveheart' star - who is currently embroiled in a custody battle with former partner over their 12-month-old daughter Lucia - denied Oksana's allegations that he attacked her while she was holding the baby, but in court documents confessed he slapped her when she became hysterical.
According to a declaration dated June 23 2010 that was filed with Los Angeles Superior Court and obtained by gossip website TMZ, Mel said the pair were arguing on January 6, 2010 when Oksana grabbed Lucia and screamed at him "Stop yelling or you will make her into a retarded brain damaged idiot!"
The 54-year-old actor claimed he was worried Lucia would suffer Shaken Baby Syndrome - neurological damage sustained to infants after being shaken - because the singer "started swinging Lucia erratically in her arms, jerking her body from side to side to keep Lucia out of my reach".
He explained in his declaration: "I slapped Oksana one time with an open hand in an attempt to bring her back to reality. I did not slap her hard, I was just trying to shock her so that she would stop screaming, continuing shaking Lucia back and forth.
"I did not hit Oksana with a closed fist, as she alleges. I did not ever punch her in the face or in the temple or anywhere else, not then or at any other time."
While Mel admitted he was wrong to slap Oksana, he said he was worried for his daughter's safety and insisted he would never harm the tot.
He said: "While I do not believe I handled the situation as well as I should have, I was worried about the rough way Oksana was shaking and tossing Lucia around. My hand never touched any part of Lucia."
Oksana has alleged her former partner knocked out two of her teeth in the argument, but the actor insists her claims are false.
He said "There was never any blood on Oksana and none of her teeth were 'broken,' although one of the false veneers from a tooth apparently did come off, I did not see that occur at the time."