Terence Crawford knocked Amir Khan down just a few punches into their fight.

The punch that finally ended it was below the belt.

Crawford retained his welterweight title by technical knockout Saturday night when Khan wasn't able to continue after being hit with a low blow in the sixth round.

Crawford threw a left hand that hit Khan on his right hip and Khan retreated toward his corner in pain. After taking a couple minutes trying to shake off the pain, his corner told the referee that Khan couldn't continue.

"I could tell I was breaking him down. It was just a matter of time," Crawford said.

It was a strange, unsatisfying ending to Top Rank's first ESPN pay-per-view card, drawing loud boos from the crowd of 14,091 at Madison Square Garden. The finish left Crawford and promoter Bob Arum with plenty of time to lobby for the fight they want next.

"The fight I want next is Errol Spence," Crawford said. "Whenever he is ready, he can come and get it."

Crawford (35-0, 26 KOs) had knocked Khan down in the first round, but the final couple rounds had been competitive, with both fighters throwing hard shots from close range.

Referee David Fields didn't appear to see the final one that hit Khan (33-5) low. Khan could have taken five minutes trying to recover, but his trainer, Virgil Hunter, made the decision before then that Khan was finished.

"I didn't want to send him back out there when he didn't have his legs," Hunter said.

Crawford was ahead 49-45 on two judges' cards and 50-44 on the other.

"I was disappointed the corner stopped the fight in that manner, but Virgil is a great coach, and he was looking out for his fighter," Crawford said. "I know he didn't want to go out like that."

Crawford started fast in the second defense of his WBO version of the 147-pound belt, throwing a short right hand to the head followed by a left that sent Khan to the canvas. He hurt Khan again late in the round and had no trouble controlling the early part of the fight.

They both threw hard shots in the fourth and Khan landed some of them in his best moments of the fight. But Crawford hit him with a pair of good lefts in the fifth and was scoring again in the sixth when his final punch accidentally drifted low.

Arum said he thought Khan could have continued.

"He had five minutes to recover," Arum said. "It was an accidental low blow. He could have recovered from it. They have a cup, right? But he was looking for a place to fall."

Khan, the 2004 Olympic silver medalist from Britain, was looking for what could have been the biggest victory of his pro career. The former 140-pound champion could have looked to fight fellow British star Kell Brook in perhaps a more lucrative and winnable match, but instead took the opportunity at Crawford, the Omaha, Nebraska, product widely considered one of the best fighters in boxing.

Hunter thought Khan had been steadying himself, even though he wasn't winning the rounds.

"I now know why Terence is one of the best pound-for-pound fighters in the world," Khan said.

The biggest fight for Crawford would be a match with Spence, the IBF champion who is also unbeaten. But Spence fights under Premier Boxing Champions, run by Al Haymon, and Arum said Haymon won't let his fighters risk losing to fighters from other organizations.

Arum criticized Haymon in the ring and then again afterward for refusing to allow a fight he said that the fighters and fans want to see.

"We want to fight Errol Spence," Arum said. "Everyone wants the fight. There is one guy stopping it, and that is Al Haymon."

More boxing news

Newsday LogoYour Island. Your Community. Your News.Digital AccessOnly 25¢for 5 months