Utilizing a reach advantage, Barthelemy (20-0, 12 knockouts, 1 no contest) kept a charging Mendez at a distance as he connected with lead left jabs. Barthelemy also closed range in the third round, scoring with lefts and rights to the body.
But fighting at tight quarters helped Mendez enjoy productive rounds in the seventh and eighth. Mendez, making his third title defense, landed combinations to the body and left hooks to the head.
Barthelemy pinned Mendez (21-3-1, 11 KOs, 1 NC) to the ropes in the ninth and scored with lefts to the head. In another close exchange later in the round, referee Tellis Assimenios deducted a point from Barthelemy for hitting below the belt.
Another punch below the belt by Barthelemy in the 10th prompted Assimenios to deduct a second point from the challenger.
With the likelihood of the scorecards narrowing because of the point deductions, Barthelemy chased Mendez and landed lefts to the head in the 11th round. Mendez, of the Dominican Republic, moved around the ring, avoiding follow-up combinations.
Barthelemy aggressively pursued Mendez in the 12th, landing combinations to the head. Mendez stood up to Barthelemy and landed short left hooks to the head.
In their first fight, Barthelemy initially was a second-round knockout winner. But Barthelemy’s two-punch combination that finished Mendez occurred after the bell.
The Minnesota boxing agency, which supervised the bout, overturned the result, making it a no-contest after an appeal from Mendez’s promotional company, Iron Mike Productions.
Former heavyweight champion Mike Tyson, who serves as Iron Mike’s president, sat at ringside for Thursday’s bout.
Barthelemy weighed the junior-lightweight limit of 130 pounds for the rematch, one more pound than Mendez.