LAS VEGAS – Shohjahon Ergashev knocked out 20 of his first 23 professional opponents and entered the ring undefeated Saturday night.

He had never, however, encountered a relentless wrecking ball like Subriel Matias. The Puerto Rican knockout artist withstood a slow start, viciously assaulted Uzbekistan’s Ergashev for three-plus rounds and forced Javon “Sugar Hill” Steward, the trainer of the mandatory challenger for his IBF junior welterweight title, to stop their fight just as the sixth round was about to begin at Mandalay Bay Resort and Casino’s Michelob ULTRA Arena.

Matias (20-1, 20 KOs) won by technical knockout and retained his title on the Showtime Pay-Per-View portion of the David Benavidez-Demetrius Andrade undercard. Referee Celestino Ruiz officially halted the action two seconds into the sixth round of their 12-round, 140-pound title fight.

Ergashev seemed to fade during a one-sided fifth round, just the way previously unbeaten Argentinean Jeremias Ponce did during Matias’ previous fight February 25 at The Armory in Minneapolis. Ponce also declined to answer the bell for the start of the sixth round.

Matias blasted Ergashev with back-to-back left hooks that forced Ergashev to hold him a minute into the fifth round. A left-right combination by Matias landed about 40 seconds into the fifth round.

Matias got the better of a violent, sustained exchange in the final 1:15 of the fourth round. Ergashev tried to hold him to stop Matias from punching, but it didn’t work.

Matias’ right uppercut snapped back Ergashev’s head about 1:10 into the fourth round. Ergashev hammered Matias with a right hook about 40 seconds into the fourth round.

Ergashev tried to tie up Matias with under a minute to go in the third round, but Matias hit him with multiple right hands while Ergashev held his left arm. Matais stung Ergashev with a jab that connected with just under 1:20 on the clock in the third round.

Matias mounted a comeback toward the end of the second round, when he landed rights and lefts and finally kept Ergashev from throwing punches.

A straight left by Ergashev landed flush a minute into the second round. Ergashev landed back-to-back right hooks about 30 seconds into the second round.

Ergashev’s right connected with about 20 seconds to go in the opening round.

The first left hand Ergashev landed knocked Matias backward, into the ropes, barely 20 seconds into the first round. Matias didn’t seem badly hurt by that shot, though.

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