Siva from 'The Wanted' -- Gets Black Eye Saving Domestic Violence Victim

Siva Kaneswaran fought off a man he says was beating a woman on the street in NYC -- and ended up catching a shiner in the process.

"The Wanted" singer was walking in Chelsea last month with his rep ... when they saw the man attacking his girlfriend. The rep tells us Siva ran over and tried to break it up, telling the man to chill out -- but the attacker yelled back, "This isn't about you."

The rep says that's when it got physical -- while Siva was trying to hold the guy back, he got clocked in the face. The attacker eventually took off, but the scuffle gave the GF enough time to run away.

We're told Siva initially wanted to keep the fight -- and his shiner -- under wraps, but is now hoping the woman will get in touch with him so he can be sure she's okay.

Siva's got a bad record with good deeds. A homeless man attacked him outside a Denver movie theater earlier this year ... when he tried to give him money.