A sore loser stabbed a 12-year-old boy in the chest, enraged that the kid was beating him in a basketball game at a Bronx park on Saturday, cops said.

The 12-year-old was up in a basketball game at the Marble Hill playground around 3:30 p.m. when his opponent slashed the boy in the chest with an unknown object, according to police.

The child was transported to Columbia Presbyterian Hospital, where he was in stable condition as of Saturday night, police said.

No arrests have been made.