MINNEAPOLIS – Brian Mendoza made the absolute most Saturday night of a high-profile opportunity that the ambitious middleweight took on short notice.

Mendoza, who was listed as a 2-1 underdog, knocked out former 154-pound champion Jeison Rosario early in the fifth round of a middleweight match Showtime televised from The Armory. Mendoza’s right uppercut dropped Rosario for the second time in the bout, three rounds after he sent Rosario to one knee with a body shot, and Rosario couldn’t continue.

Referee Mark Calo-oy stopped the action 35 seconds into the fifth round of a scheduled 10-rounder.

Rosario was supposed to box unbeaten Cuban southpaw Yoelvis Gomez (6-0, 5 KOs) on Saturday night. Mendoza replaced Gomez on approximately 10 days’ notice, once Gomez sustained an injury to his right wrist while training.

The 28-year-old Mendoza (21-2, 15 KOs) recorded by far the most noteworthy win in eight years as a pro. Before he knocked out Rosario, the 28-year-old Las Vegas resident’s career came off track because he lost unanimous decisions to junior middleweight contender Jesus Ramos (10 rounds) and Larry Gomez (eight rounds).

Rosario was supposed to box unbeaten Cuban southpaw Yoelvis Gomez (6-0, 5 KOs) on Saturday night. Mendoza, an Albuquerque native, replaced Gomez on approximately 10 days’ notice, once Gomez sustained an injury to his right wrist while training.

The 27-year-old Rosario (23-4-1, 17 KOs) has lost by knockout or technical knockout four times. Undefeated, undisputed 154-pound champ Jermell Charlo and contender Erickson Lubin knocked him out in back-to-back bouts over a nine-month span before he beat three nondescript opponents by TKO in his native Dominican Republic prior to meeting Mendoza.

On Saturday night, a vicious right uppercut by Mendoza dropped Rosario to his gloves and knees barely 25 seconds into the fifth round. A disoriented Rosario reached his feet, but he stumbled and fell again, which forced Calo-oy to end their fight.

A right-left combination by Rosario backed up Mendoza with 1:10 to go in the fourth round, but Mendoza made Rosario respect his power later in the fourth round. Mendoza and Rosario got tangled up and tumbled to the canvas together a little less than 30 seconds into the fourth round.

Rosario’s right hand landed, but Mendoza took it well with about 15 seconds remaining in the third round. Mendoza drilled Rosario with a left hook up top as Rosario pressed forward almost 1:20 into the third round.

Mendoza’s well-placed left hook to the body dropped Rosario to one knee with about 55 seconds to go in the second round. Rosario waited almost until Calo-oy counted to 10 before he got up, but he managed to move and hold his way to the end of the second round.

Mendoza caught Rosario with a right hand in an exchange 1:10 into the second round.

With just over 30 seconds on the clock in the first round, Calo-oy warned Rosario for hitting Mendoza with two punches – a right to his shoulder and a lesser left to the middle of his face – after the veteran referee called for a break. Rosario caught Mendoza with two left hooks after they clinched a few seconds after the midway mark of the opening round.

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