The developing junior welterweight contender is right-handed, but he fought almost exclusively from a southpaw stance on his way to stopping Bryce Mills in the fourth round on the Xander Zayas-Jaron Ennis undercard at Barclays Center in Brooklyn.

Vargas (18-0, 15 KOs) was credited with a questionable knockdown late in the third round before he overpowered Mills a round later.

A stunning straight left by Vargas knocked Mills to the canvas awkwardly early in the fourth. Mills made it to his feet, but Vargas switched to orthodox and hurt him again with a right hand to stagger him.

Referee Ricky Gonzalez stepped between them as Vargas continued to unload hard shots on Mills, a former kickboxer who lost by knockout for the first time in 24 professional fights. The official time of the stoppage was 1:17 of the fourth.

Vargas, The Ring’s reigning “Prospect of the Year,” continued to build his way toward a title shot. He entered his impressive victory over Mills as the WBO’s No. 2 contender for Shakur Stevenson’s 140-pound title.

Las Vegas’ Vargas, the youngest son of former junior middleweight champ Fernando Vargas, ended Mills’ 16-fight winning streak. Mills (22-2, 9 KOs), of Liverpool, New York, hadn’t lost since a six-round, split-decision defeat to Ryan Pino (then 8-7-2) in October 2021.

Prior to the finish, Gonzalez credited Vargas for a knockdown with just over 20 seconds remaining in the third round. The replay showed, however, that Vargas pushed him down by the back of his head as their feet got tangled.

Mills scored two right hands with less than 50 seconds to go in the second round, but Vargas came back to nail him with a straight left.

Vargas told DAZN’s Chris Mannix afterward that he saw surprise on Mills’ face when he turned southpaw as soon as the opening bell rang. Mills still pressured him and landed several flush punches before Vargas became more comfortable, fought from a distance and opened up toward the end of the first round.

Keith Idec is a senior writer and columnist for The Ring. He can be reached on X @idecboxing