Errol Spence Jr. was leading Yordenis Ugás on the scorecards when, in the sixth round of their welterweight title unification bout, Ugás clipped Spence with the cleanest single shot of the fight to that point, a looping right hand that connected where the jaw meets the neck.

The impact ejected Spence’s mouthpiece onto the canvas of the ring at AT&T Stadium in Arlington, Texas. Then Ugás landed another punch, driving Spence toward the ropes.

Spence, 32, who entered Saturday with the World Boxing Council and International Boxing Federation titles, had rebounded from career-threatening injuries. In October 2019, he spent a week in a hospital after a car crash. Last year, he had to pull out of a title fight against Manny Pacquiao because of a partially torn retina in his left eye.

But before that fraught sequence Saturday night, Spence, who was born on Long Island and raised in Dallas, had never appeared vulnerable in the ring.

His response? A quick regrouping, and more of the aggressive offense that had allowed him to win most of the opening rounds. He closed the round moving forward, throwing rights and lefts to Ugás’s midsection, some of the 70 body punches he landed in the match.

Midway through Round 10, the referee, Laurence Cole, halted the bout at the urging of the ringside doctor, who had concluded it was unsafe for Ugás to continue fighting with his right eye swollen shut.

With the win, by technical knockout, Spence answered questions about whether he had fully healed from the car crash and eye surgery. He outclassed and beat up a boxer, Ugás, who shared Spence’s penchant for mixing tactical boxing with toe-to-toe exchanges.

And Spence annexed the World Boxing Association title, which means one of boxing’s glamour divisions is one fight away from having a single, undisputed champion. Before he even left the ring, Spence issued a verbal challenge to the World Boxing Organization welterweight champion, Terence Crawford.

“Everybody knows who I want next,” Spence said in the ring after the fight. “I want Terence Crawford.”

Crawford, who was not at ringside, live-tweeted Saturday’s main event and ended his social media session with some trash talk aimed at building anticipation for a fight boxing fans have long wanted.

“Keep my belts warm,” Crawford tweeted at Spence. “I’m coming to grab ’em later this year.”

From a purely competitive standpoint, a matchup of Spence and Crawford, widely considered the welterweight division’s two best fighters, has long made sense. But professional boxing is also a business, which has complicated pairing the two fighters. Spence is aligned with Premier Boxing Champions, while Crawford, until November, was signed with Top Rank, a rival promotional outfit.

But now Crawford is a free agent, and Spence’s stock is rising after his emphatic victory. Spence, who is 28-0, might not enjoy the mainstream fame of some of his welterweight predecessors, like Floyd Mayweather Jr. and Pacquiao, but he sells pay-per-views and tickets — 39,946 spectators attended Saturday’s card.

“When we look at the history with Errol Spence, he’s pretty reliably at least 300,000 buys,” Stephen Espinoza, the president of Showtime Sports, the pay-per-view partner for Saturday’s card, said in an interview before the fight. “He’s generating a gross of at least $20 million every time out, just in pay-per-view revenue. That’s an elite figure.”

Spence also delivers action.

Early in their bout, Ugás scored with jabs and right hands to the body, disrupting Spence’s advances and countering his big punches. But as rounds passed, Spence found his rhythm and increased his output, denying Ugás clear chances to counter. Where Ugás landed punches from midrange, Spence worked from the outside in, prodding with his right jab until he could move close enough to rip punches to Ugás’s body and head.

In Round 6, Ugás created enough space to land that heavy right hand. He believed, momentarily, that he had turned the fight.

“I thought I had a chance there,” Ugás said in the ring after the bout. “But he’s a great fighter. He recovered.”

By then, Ugás’s right eye was swelling. In the seventh, a left uppercut made Ugás retreat. Spence pursued him, landing an overhand left and a roundhouse as Ugás covered up. One round later, the ringside doctor halted the action to examine Ugás’s eye, but cleared him to continue.

Early in Round 9, Spence leaned to his right and ripped a right hook to Ugás’s torso, just above the red belt line of his trunks. Just below Ugás’s waist, his white trunks were tinted pink with traces of blood, presumably Ugás’s.

The next round, the doctor paused the fight again, took another look at Ugás’s misshapen face, and advised the referee to stop the fight. He did.

According to CompuBox, Spence landed 216 of 784 punches, compared with 96 of 541 for Ugás.

For Spence, the bout marked his first stoppage win since 2018, another sign that he has recaptured the dominance he showed before the car wreck. For the boxing public, the result means real progress toward the most significant welterweight fight of this generation.

“It’s strap season,” Spence told reporters at a news conference after the fight. “I got one more belt to get.”