Edwin De Los Santos was training for a non-televised undercard bout on a separate show when he got the late call.

The Dominican knockout artist rose to the occasion, scoring an upset third-round stoppage of previously unbeaten lightweight Jose Valenzuela. De Los Santos survived a second-round knockdown to score two of his own in forcing the stoppage at 1:08 of round three in their Fox Sports Pay-Per-View opener Sunday evening at Crypto.com Arena in Los Angeles.

Valenzuela was spared the displeasure of being left without an opponent thanks to De Los Santos remaining on standby for nearly a month. De Los Santos was told to be ready if originally scheduled former WBA junior lightweight titlist Jezreel Corrales was unable to secure a travel visa which turned out to be the case.

De Los Santos didn’t waste any time in proving that he was far beyond a typical late replacement. The 22-year-old southpaw from Santo Domingo caught Valenzuela off guard with a four-punch combination. Valenzuela was forced to ease up on his intended aggressive attack, going to the jab and keeping his distance in respecting De Los Santos’ power. De Los Santos caught an onrushing Valenzuela with a jab, throwing a left hand behind it to highlight a strong opening round.

It wouldn’t hold a candle to the rest of the fight.

Valenzuela was still wild in his attack but able to get by on his pure power. De Los Santos managed to land a left hand but was rocked by a counter right hook by Valenzuela. An ensuing volley by Valenzuela proved to be window dressing as De Los Santos was already on his way down for the bout’s first knockdown.

De Los Santos immediately responded upon rising from the canvas, drilling Valenzuela with a right hook. Valenzuela was badly rocked as De Los Santos with a volley of punches to send the unbeaten Mexican to the canvas and nearly through the ropes. De Los Santos was caught up in the moment, continuing to throw punches while Valenzuela was down which drew the scorn of referee Ray Corona who deducted a point from his scorecard.

De Los Santos closed the show in style in round three. A left hand clipped Valenzuela on the chin and forced him to a knee. Corona warned Valenzuela upon rising that additional punishment would result in an immediate stoppage. The third man stayed true to his word, as an ensuing flurry by De Los Santos left Valenzuela defenseless and soon with his first defeat as he falls to 12-1 (8KOs).

The win is the second straight for De Los Santos (15-1, 14KOs) after suffering his first defeat earlier this January. The hard-hitting prospect admitted that he had flaws to correct, which he has emphatically improved as shown in back-to-back early knockout wins.

Valenzuela-De Los Santos opened a four-fight PPV. Headlining the show, former unified heavyweight titlist Andy Ruiz (34-2, 22KOs) faces two-time title challenger Luis Ortiz (33-2, 28KOs) in a scheduled twelve-round WBC heavyweight semifinal eliminator.

Jake Donovan is a senior writer for BoxingScene.com. Twitter: @JakeNDaBox