Daniel Jacobs smiled in his corner after an action-packed third round, looking pleased to be in a tough fight.
It wasn't clear he would win it until he knocked Maciej Sulecki down with the kind of punch he wants to throw at the middleweight division's biggest names.
The 12th-round knockdown helped Jacobs win a unanimous decision Saturday night, strengthening his hopes of getting another title shot.
Jacobs pulled out a competitive fight, winning by scores of 117-110, 116-111 and 115-112 and handing the Polish fighter his first loss.
Jacobs (34-2-0) became the mandatory challenger for the WBA 160-pound title, giving the popular Brooklyn fighter and cancer survivor hopes of a chance to avenge his loss to Gennady Golovkin from last year.
"I truly believe that I won the fight with 'GGG' but the judges saw it differently. This is boxing and I know this is what you sign up for when you first lace up the gloves," Jacobs told Sky Sports.
"I would come forward and be the aggressor more in a rematch. The fact we nullified him down to a Golovkin we hadn't seen before and it was me who landed more power shots when he is known as the devastating puncher says a lot.
"I would tune things differently but be the same mentally. I proved I do belong and I will take it in my hands a little more if we go for a second time."
Jacobs had a much tougher time with Sulecki (26-1), who seemed to gain confidence as the fight went on and was getting the better of some of the action in the late rounds until Jacobs caught him with a quick right to the head early in the 12th, sending Sulecki to the canvas as Brooklyn fans roared for the hometown fighter.
There had been chants of "Brook-lyn, Brook-lyn" earlier in the bout from the local fans that made up the announced crowd of 7,892 at Barclays Center. But the vocal section of Polish fans grew louder in the later rounds as their fighter rallied.
They had traded hard shots across the final seconds of the third, Jacobs smiling afterward as if satisfied by the action. Disappointed that Luis Arias went defensive and he had to settle for a decision in his last bout, Jacobs seemed to enjoy being in a real fight Saturday.
He won it by finding a way to be just a bit quicker than Sulecki in their exchanges. But promoter Eddie Hearn has been calling Jacobs the best middleweight in the world, and at times Saturday he was barely the best middleweight in the ring.
