But in Round 2, a quick exchange of punches ended with a short right jab from Crawford that put an off-balance Spence to the canvas. The knockdown marked the first time either fighter had been dropped in his professional career but in the moment it seemed brief and inconsequential. Spence opened the next round on offense, as if to prove the punch had not damaged him.

As the fight wore on, however, Crawford’s superior timing and one-punch power had become apparent.

In Round 7, Spence gathered himself to throw a looping left. As the punch traveled toward Crawford’s head, Crawford fired a short, sharp right hook that dropped Spence a second time. Just before the bell, a double right hook knocked Spence off his feet again.

A flurry of hard punches in Round 9 prompted the referee, Harvey Dock, to stop the fight.

For Crawford, the result was a lesson on the value of turning defense into offense.

“Our main focus was the jab,” he said. “Take away his best attribute and the rest is history.”

From here, another Spence-Crawford fight is possible, even after the one-sided result. A clause in the contract allows the loser to call for an immediate rematch. One or both fighters might also move up to the 154-pound junior middleweight class. Spence had hinted that the Crawford bout would be his last in the 147-pound welterweight division.

“We gotta do it again,” Spence, now 28-1, said in the ring after the fight. “I’ll be a lot better.”

If Crawford changes weight classes, the welterweight belts would likely become vacant, setting off a scramble for championships among contenders like Ugás, Cody Crowley, and Jaron Ennis, the standout contender from Philadelphia.