A resilient Angel Fierro changed his life Thursday night.

The Mexican underdog survived a knockdown apiece in each of the first two rounds and knocked out Alberto Machado in the sixth round of their televised main event in Salinas, Puerto Rico. Fierro, who took this tough lightweight fight on two weeks’ notice, blasted Machado with a sweeping left hook that knocked Machado to the canvas 35 seconds into the sixth round.

Machado attempted to get up, but referee Jose Hiram Rivera determined that the former WBA super featherweight champion shouldn’t continue. Rivera stopped their scheduled 10-rounder 47 seconds into the sixth round.

Fierro, 22, was down by the same score, 48-45, on all three scorecards when he knocked out Machado in a fight NBC Sports Network aired as part of its “Ring City USA” series.

Tijuana’s Fierro (18-1-1, 14 KOs) became the second opponent to knock out the 30-year-old Machado (22-3, 18 KOs). The Puerto Rican southpaw suffered back-to-back knockout defeats to American Andrew Cancio (21-5-2, 16 KOs) in 130-pound title fights in 2019.

Machado was supposed to face San Antonio’s Hector Tanajara (19-0, 5 KOs), but Tanajara pulled out of their fight due to an undisclosed illness.

Before ending their fight in the sixth round, Fierro gained more momentum as he came back during the fifth round.

Fierro nailed Machado with a right hand about 30 seconds into the fifth round. Fierro applied pressure for the rest of that fifth round and had some success, especially when they fought in the center of the ring.

Fierro landed a right hand with just over two minutes to go in the fourth round. He began backing up Machado at that point in the fight and showed Machado that he wouldn’t go away as easy as it might’ve seemed in the first two rounds.

Fierro drilled Machado with two more right hands and a left as the fourth round came to a close.

Machado landed several right hands to Fierro’s body that slowed him down. Fierro managed to avoid a knockdown in that third round, unlike each of the first two rounds.

Another quick, precise right hook by Machado knocked Fierro to one knee with 15 seconds left in the second round. Fierro bounced right back to his feet, but he went down for the second time in two rounds.

Machado’s left hand to Fierro’s body seemed to affect Fierro with just over 1:40 remaining in the second round.

Machado caught Fierro with a quick right hook that sent him to the canvas with 1:19 to go in the first round. Fierro quickly reached his feet and didn’t seem hurt from that flash knockdown as the round continued.

That marked just the second time Fierro went down during his 20-fight pro career.

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