Roberto Valenzuela Jr. was the supposed puncher entering his fight against Xander Zayas on Friday night.

It was Zayas, however, that proved to be too strong for the rugged Mexican veteran. The 21-year-old junior middleweight produced two first-round knockdowns, nearly another knockdown in the fourth round and bloodied Valenzuela’s nose to the point referee Mark Nelson stopped their scheduled 10-round, 154-pound bout in the fifth round.

Their co-feature on the Luis Alberto Lopez-Joet Gonzalez undercard was officially stopped 42 seconds into the fifth round at American Bank Center in Corpus Christi, Texas.

Zayas, a Puerto Rican fighter from Sunrise, Florida, improved to 17-0 and recorded his 11th knockout. Valenzuela (21-5, 20 KOs) lost by technical knockout for the second time in his six-year professional career.

A jarring jab by Zayas knocked Valenzuela backward about 20 seconds into the fifth round. Nelson halted the action after Zayas nailed him with a left uppercut about 20 seconds later.

A ringside physician took a close look at the cut across Valenzuela’s nose during the middle minute of the fourth round. He allowed the action to continue, but Nelson called for another break with 32 seconds to go in the fourth round.

The doctor again allowed Valenzuela to continue.

A right hand by Zayas buzzed Valenzuela soon thereafter, but Valenzuela held one of the ropes to keep from going down with just under 20 seconds on the clock in the fourth round.

A composed Zayas picked apart Valenzuela throughout the third round.

A sweeping left hook by Zayas landed with 1:20 to go in the third round. A cut opened on the bridge of Valenzuela’s nose earlier in the third round.

A stiff jab by Zayas made Valenzuela reset his feet with approximately 30 seconds to go in the second round. Zayas landed a counter left hook with about 1:15 on the clock in the second round.

Zayas scored two knockdowns during the first round.

The second knockdown was controversial because Zayas’ right hook knocked Valenzuela to the canvas with 52 seconds remaining in the opening round after their legs got tangled. Valenzuela was already falling to the canvas when Zayas hit him.

Valenzuela complained to Nelson once he reached his feet, but Nelson counted it as a knockdown.

A quick left hand by Zayas knocked Valenzuela to the canvas with 1:53 to go in the first round. A surprised Valenzuela answered Nelson’s count at seven and pawed at his nose once the action resumed.

Keith Idec is a senior writer/columnist for BoxingScene.com. He can be reached on Twitter @Idecboxing.