Teofimo Lopez Jr. dethroned Vasyl Lomachenko as he became the unified lightweight champion by unanimous decision in Las Vegas.

All eyes were on the MGM Grand, where Lomachenko put his WBA, WBO and WBC belts on the line in the blockbuster unification bout against IBF holder Lopez.

Lopez (16-0) emerged victorious over 12 rounds on Saturday, the 23-year-old completing an upset against pound-for-pound Ukrainian star as he unified the lightweight division inside the Las Vegas bubble.

The judges scored the fight 116-112, 119-109 and 117-113 in favour of unbeaten American Lopez, who snapped Lomachenko's (14-2) 13-fight winning streak after withstanding a late flurry to become the youngest four-belt champion since the WBO was founded in 1988.

"I'm a fighter," said Lopez afterwards. "I gotta dig in deep. I knew he was coming. I didn't know if they had him up on the scorecards or not, and I love to fight.

"I can bang, too. I don't care, man. I'll take one to give one. That's what a true champion does. I find a way to win."

It was a clash to decide the number one lightweight and a showdown between two fighters at contrasting stages of their careers.

Lomachenko had the pedigree heading into the bout, stemming back to a glittering amateur career that included two Olympic gold medals, through to winning world titles in three different divisions in the paid ranks. 

Lopez, meanwhile, had long been talked about as boxing's next big star, long before brutally taking the IBF title from Richard Commey inside two rounds last December.

Lomachenko was slow out of the blocks as Lopez took control of the first half of the fight, outworking the 32-year-old with his speed and pinpoint accuracy.

Out of sorts, Lomachenko – back in action following a 14-month layoff – eventually came into the fight in the eighth round but by that time, the damage had already been done.

Sensing he was behind, Lomachenko ramped up the pressure with a late rally in the championship rounds, however, Lopez landed significant shots to halt his opponent and become the new lightweight king.