"I've never seen anything like this. He gets these guys, frustrates them, and they quit because they can't answer back," Arum said of Lomachenko. "You're seeing something very special. I've seen great fighters ... nothing like this. None of them."
Rigondeaux at first blamed the injury, but was then met by boos from the fans and changed his story.
"He's a very technical, quick, explosive fighter. He is an excellent boxer," Rigondeaux said.
His promoter, Dino Duva, credited Lomachenko for his talent, saying, "He frustrates them so bad they don't know what to do."
Duva said Rigondeaux's hand pain worsened in the third round and he was hospitalized afterward for an examination.
"Where did he hurt his hand? He didn't hit him with a punch," Arum cracked after punch statistics showed Rigondeaux didn't land more than three punches in any round. "Where'd he hurt it, in the dressing room?"
The undercard included a convincing second-round technical-knockout victory by 2016 Olympic silver medalist Shakur Stevenson of nearby Newark, N.J., against mismatched Oscar Mendoza (4-3) of Santa Maria, Calif.
"Everything I threw was landing," Stevenson (4-0, two KOs) said as Mendoza offered little resistance to the top prospect whose skill was sharpened by spending time in training camp with Lomachenko.
"There's been a lot of talk about me holding. I've never been a fighter who holds. I'm a fighter. I learned a lot (from Lomachenko). You still haven't seen the best of me."
Ireland's Michael Conlan could say the same thing after he experimented with a southpaw stance and cruised to victory by three 60-54 scores over Argentina's Luis Fernando Molina (4-4-1).
Earlier, Los Angeles-trained 2016 U.S. Olympian Mikaela Mayer improved to 4-0 with a majority decision victory over New York's Nydia Feliciano (9-9-3).
Puerto Rico's unbeaten super-featherweight Christopher Diaz knocked down replacement opponent Bryant Cruz in the first round with a power punch to the nose, and dropped him again in the second by battering him to the body, weakening the legs.
After a doctor's review, Cruz's legs went out on him 37 seconds into the third, as Diaz delivered a power shot and improved to 22-0.
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