Unbeaten junior lightweight prospect Rances Barthelemy was looking Friday for the breakthrough performance his promising career has lacked.

Against 130-pound titlist Argenis Mendez at the Target Center in Minneapolis, Minn., Barthelemy, 27, provided just that when he scored a pair of knockdowns en route to a dominant second-round knockout.

The victory came, however, with a bit of controversy.

Barthelemy (20-0, 13 KOs) hit Mendez with a flurry of flush shots as the final seconds ticked away to end of Round 2. But two -- if not all three -- of the finishing blows that forced the final knockdown were delivered after the bell had sounded.

Referee Pete Podgorski counted out Mendez, 27, with no time left in the round, setting off a wild celebration from Barthelemy, who won his first world title.

Argenis Mendez was knocked down for the first time in his career before losing his 130-pound title to Rances Barthelemy via second-round knockout. Reynaldo Sanchez/Mpsportimages.com

"The key to this fight was patience. I knew about his abilities and skills, so I had to respect that," said Barthelemy to ESPN's Bernardo Osuna, who translated after the bout. "I'd have to see it again, but I think that [the knockout punch] was in the moment. My punches were flying as the bell was ringing. That's how I see it."

Former heavyweight champion Mike Tyson, the promoter of Mendez (21-3-1, 11 KOs), said after the fight that he plans to appeal the ruling and seek a rematch. The state of Minnesota does not allow instant replay during a fight.

"I'd be happy to give him a rematch," Barthelemy said. "I'm all about fighting the best. I'll fight anyone."

Key moment: Barthelemy set the stage for Mendez's exit by knocking down the Dominican fighter late in the second round on a perfect three-punch combination. Barthelemy packaged a body shot, stinging jab and hard left hook to floor Mendez for the first time in his career.

We've got your number: 3. That's the number of punches Mendez landed in a first round dominated by Barthelemy, who buckled his opponent with a pair of counter left hooks placed perfectly between Mendez's guard.

Last word: The blame for the controversial finish should fall more on the referee for failing to jump in than on Barthelemy, who was impassioned in his pursuit of the knockout as the final seconds ticked off to end Round 2. If anything, it was a lack of passion and urgency at times that had held the Cuban-born fighter back from showing how good he can be in some previous outings. Friday was a different story, as Barthelemy made an impact early with crisp, hard counter shots and never let up. While Mendez likely deserves a rematch for his troubles, Barthelemy's statement was still made to the remainder of the 130-pound division.