American Shakur Stevenson dominated Teofimo Lopez to secure the WBO light-welterweight belt by unanimous decision at Madison Square Garden.
The 28-year-old, who has won all 25 of his professional bouts, is now a four-weight world champion, with the judges scoring the fight 119-109 119-109 119-109.
Post-fight tensions were high as Stevenson called out Conor Benn, who aggressively entered the ring and exchanged words.
"You're too small for me," Benn told DAZN.
"We can do it next. Come up to welterweight with the big dogs. You're a small, little man."
Following a rematch victory over Chris Eubank in November, Benn reiterated his intention to drop down to welterweight and take on the division's world champions.
The 29-year-old jumped up two weight classes to fight Eubank, with the pair agreeing to a rehydration clause that prohibited putting on more than 10lb between Friday's weigh-in and Saturday morning.
Benn has fought at welterweight and middleweight during his career, while Stevenson has moved up from featherweight to light-welterweight.
"I like the beef and story behind it," Stevenson said.
"I am a businessman at the end of the day and he did a rehydration clause with Chris Eubank, who was in the ring half-dead. Why can't he do the same thing?"
Both fighters are signed with Matchroom Boxing, which could make agreeing on a weight easier.