Photos: Michael Conlan, Shakur Stevenson, Diaz, Jennings Win

The Theater, Madison Square Garden, New York City - Former Olympic medalists Shakur Stevenson and Michael Conlan were among the winners on the undercard. Stevenson (4-0, 2 KOs) outclassed Oscar Mendoza (4-3) before referee Sparkle Lee stopped the featherweight bout midway through the second round. Fighting near his hometown of Newark, New Jersey, the southpaw who won silver in 2016 landed sometimes three or four punches in rapid succession before Mendoza could get out of the way.

Conlan (5-0) delighted the contingent of Irish flag-waving fans with a unanimous decision victory over Argentina's Luis Molina (4-4-1), winning every round of the six-round bout in his first pro victory that didn't come by stoppage.

Conlan peppered Molina with combinations to the body and left uppercuts to the chin in the arena where he made his professional debut last year on St. Patrick's Day. Arum also plans to have the 2012 bronze medalist from Belfast fight again next year on the March 17 holiday.

Also picking up impressive knockouts wins on the card were heavyweight Bryant Jennings and unbeaten Puerto Rican Christopher Diaz, who demolished Bryant Cruz.

In the main event of the card, Vasyl Lomachenko continued his meteoric rise up the boxing ladder, retaining his WBO junior lightweight title Saturday night after challenger Guillermo Rigondeaux quit on his stool after six rounds.

The 29-year-old Lomachenko was awarded the victory when Rigondeaux elected not to come out for the seventh round in the first world title professional showdown between two multiple Olympic gold medal winners.

The outclassed Rigondeaux becomes the fourth straight boxer to quit mid-fight against Ukrainian Lomachenko.

Lomachenko improved to 10-1 as he handed the Cuban defector the first loss of his career in front of a crowd of 5,100 at the Madison Square Garden Theater.

Lomachenko humiliated Rigondeaux, using his size and hand speed to dominate every round except the first.

He grew increasingly frustrated with Rigondeaux's tactics which included low blows and more clutching and grabbing than throwing punches. Lomachenko landed 55 punches overall while Rigondeaux landed just 15.

Rigondeaux, who was booed loudly after the fight, looked the much smaller of the two fighters as the 37-year-old moved up two weight classes to challenge for the title.