Even though he suffered a cut over his right eye during the bout, O'Leary remained highly regarded within the 140lbs division thanks to his skillful jab and short punches.
Matirosyan faced O'Leary with a record of 16-1 (10 KOs).
He started the fight cautiously but grew more confident as it progressed. However, Matirosyan was knocked down in the first round by a short left hook from O’Leary and later suffered a cut caused officially by a punch after initially thought to be from a clash of heads.
O'Leary started strong by dropping Matirosyan early but got cut over his right eye in round three.
By round six, both boxers displayed cuts but continued vigorously.
A significant attack was launched by O’Leary in round seven.
The decisive moment came in round nine when O’Leary landed another clean left hook that Matirosyan couldn't recover from.
Other results for today's Magnificent Seven Show: