LAS VEGAS – Jesus Ramos wouldn’t allow Vladimir Hernandez to pull off another upset Saturday night.

The rising junior middleweight prospect rocked Hernandez with a left hand in the sixth round that suddenly changed what was a competitive contest on the Keith Thurman-Mario Barrios undercard. That shot buckled Hernandez’s legs and enabled Ramos to pounce on his vulnerable opponent.

The 20-year-old Ramos landed several more power punches, including a right-left combination that knocked Hernandez into the ropes. Referee Mike Ortega stepped between them soon thereafter because Hernandez clearly wasn’t in condition to continue.

The official time of the stoppage was 2:21 of the sixth round in a scheduled 10-rounder FOX Sports Pay-Per-View televised from Mandalay Bay Resort & Casino’s Michelob ULTRA Arena.

Ramos, a strong southpaw from Casa Grande, Arizona, improved to 18-0 and recorded his 15th knockout. Hernandez (13-5, 6 KOs) – a 32-year-old southpaw from Ciudad Lerdo, Mexico, who upset former 154-pound champ Julian Williams in his last fight – lost by knockout or technical knockout for just the second time in his 12-year pro career.

In the round before the bout abruptly ended, the fifth round was another back-and-forth three-minute period fought almost exclusively on the inside that could’ve gone either way.

Ramos was more effective inside with his left hand during the fourth round than he was during the previous two rounds.

Hernandez landed the cleaner punches on the inside during the third round, when he made Ramos miss more than vice versa.

Hernandez landed back-to-back left hands inside on Ramos early in the second round and got the better of the action in those three minutes. Ramos and Hernandez landed their fair share of punches in what was a close opening round.

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