DALLAS — Terence Crawford (20-0) knocked out Mexico’s Alejandro Sanabria (34-2-2) with a left hook in the sixth round to take the NABO lightweight title on the undercard of Saturday’s main event at American Airlines Center.The knockout was the 16th in the career of the Omaha, Neb., resident.“He kept blocking my jab,” Crawford said. “So I faked a jab and threw a short hook and I felt that power go up my right arm.”The bout gained steam in the fourth round when Crawford started landing punches to Sanabria’s head and body. Crawford dominated the fifth round and needed 17 seconds in the sixth to land the final blow.Lopez packs punchDallas resident Tony Lopez (4-0) knocked out Jonathan Hernandez (1-3-1) in the fourth round with a vicious left-handed punch that left Hernandez sprawled on the mat, his head dangling over the edge of the ring.The 19-year-old Lopez, who received loud cheers from the AAC crowd, dominated all four rounds of the super bantamweight bout. Hernandez was backpedaling most of the fight.Lopez’s knockout blow came 33 seconds into the fourth round.‘Nightmare’ prevailsFormer U.S. Olympian Vanes Martirosyan overwhelmed Ryan Davis (24-11-3) to earn a second-round knockout and improved to 33-0-1.Nicknamed “Nightmare,” Martirosyan lived up to his moniker early in the super welterweight bout.The Glendale, Calif., native first knocked down Davis with a flurry of punches three minutes into the second round, and then ended the fight a minute later by again knocking down his overmatched foe.Pair goes distanceMikael Zewski (20-0) needed all eight rounds of his welterweight fight to defeat Damian Frias (19-8-1) in a unanimous decision.Zewski dominated the first four rounds and appeared to have Frias on the ropes several times. But Miami native Frias, 36, battled back in the fifth and took three of the next four rounds.Despite knocking down a bloody Zewski in the final round, Frias’ efforts weren’t enough.Pena overwhelmedWelterweight John Karl Sosa (7-0) remained undefeated with his second-round knockout of Ramon Alejandro-Pena (7-3).From the first bell, it was apparent the 20-year-old Puerto Rican was too quick for the 33-year-old Pena.Sosa ended the fight 1 minute, 54 seconds into Round 2 with a left-hook knockout punch to Pena’s body.