NEW YORK – Harley Mederos became the first of seven professional opponents to stop Julio Madera late Saturday afternoon.

The lightweight prospect from Brooklyn remained unbeaten by defeating Madera by sixth-round technical knockout on the Amanda Serrano-Erika Cruz undercard at Madison Square Garden’s Hulu Theater. Mederos (5-0, 4 KOs) buzzed Madera twice with left hooks in the opening round and spent the ensuing four-plus rounds drilling his game Mexican opponent with left hooks and right hands.

A New York State Athletic Commission physician examined Madera after each of the final three completed rounds. Once Mederos resumed his assault early in the sixth round, referee Eric Dali stepped between them to prevent Madera from taking unnecessary punishment in a fight he clearly had very little chance to win.

Dali stopped their six-rounder just 25 seconds into the final round.

Mexico City’s Madera slipped to 5-2 (3 KOs). Madera dropped another lightweight prospect, Marc Castro, in the second round of a six-round fight Fresno’s Castro (9-0, 6 KOs) came back to win by unanimous decision last March 5 at Pechanga Arena in San Diego.

Madera took a lot of punishment during the fifth round. A doctor took a close look at him in his corner before Madera was allowed to start the sixth round.

A right-left combination by Mederos stopped Madera from coming forward with just under a minute to go in the fourth round. Mederos caught Madera with two hard right hands later in the fourth round.

Mederos continued to hammer Madera with flush punches during the third round, including a hard right and that landed after the bell. Mederos battered Madera with left hooks & right hands throughout a one-sided second round that left Madera with a bloody nose.

Mederos sat down on his punches as soon as their bout began, seemingly intent to record a knockout before his hometown fans.

Mederos knocked Madera off balance with a left hook in the final minute of the first round. Dali warned Mederos for hitting Madera behind his head twice thereafter, but Mederos wobbled Madera with another left hook just before the first round concluded.

In the first fight Saturday, Aaron Aponte bounced back from the lone blemish on his professional record. The 21-year-old Aponte won an eight-round unanimous decision against Joshua Rivera.

Aponte (7-0-1, 2 KOs), of Hialeah, Florida, shut out Rivera (8-2, 3 KOs) by the same score, 80-72, on the cards of judges Ron McNair, Allen Nace and Martha Tremblay. Rivera, of La Mesa, California, has lost two of his past three fights.

Rivera pressed forward for much of their bout, but Aponte consistently landed the cleaner punches to his head and body.

Aponte fought for the first time since his eight-round split draw with Fernando Molina (then 8-0) on the Canelo Alvarez-Gennadiy Golovkin undercard September 17 at T-Mobile Arena in Las Vegas.

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