Leapai was destroying Nigerian scrapper Izonritei through the opening rounds and a finish seemed all but certain.
With his opponent covering up against the ropes as he searched for the knockout blow in the third round, Leapai opened up a huge cut over Izonritei's eye.
The referee stopped the action and ruled the cut had been opened by a stray elbow.
Leapai, who fought Wladimir Klitschko three years ago, thought he'd won the fight, but it was called a technical draw because the bout hadn't yet reached the fourth round.