He did it with a body shot that landed legally, though Judah claimed it was a low blow.
No matter, said Khan, who was landing big blows even before the punch that put Judah down.
"If it had gone another few rounds, I would have knocked him out with a clean shot," Khan said.
Khan was dominating the fight when he threw a right hand that landed just at the belt line of Judah, who went to the canvas. Judah stayed there on his knees as referee Vic Drakulich counted him out at 2:47 of the fifth round.
Judah acted as though he was surprised to be counted out, but got up and went to his corner as Khan celebrated with his cornermen. Judah had earlier complained about being butted by Khan and was bleeding from his nose and cuts to his face.
"It was a low blow. I was trying to get myself together," Judah said. "That was self-defense right there." The win was an impressive one for Khan, the former Olympic silver medalist who likes to call himself the best pound-for-pound boxer in England. He came in as a 5-1 favorite, and had no trouble against the southpaw Judah, using his quickness to beat him to the punch in almost every exchange.
Khan won the first four rounds on all three ringside scorecards.
"I think my speed overwhelmed him, along with my power," Khan said. "I thought I was hurting him and it was only a matter of time." The end came when Khan landed a right hand that appeared to be legal, but just barely. Judah went down and stayed there with his back to Drakulich as the referee counted him out.
Khan, who improved to 26-1 with 18 knockouts, was fighting in the same ring where he engaged in a brutal slugfest last December with Marcos Maidana, a bout that was voted fight of the year by boxing writers. Khan won that fight narrowly, but was lackluster in his last title defense in April against Paul McCloskey in his hometown of Manchester.
"We trained hard and I was in the best condition of my life," Khan said. "Zab is a great fighter, but he was a little awkward. I knew he was getting hurt but he kept moving away and ducking." Khan's promoter said the British fighter would fight again Dec. 10 at 140 pounds before moving up to 147 pounds with a fight next spring that will likely be held in his hometown of Manchester.
"Then we'll go and get one of the big boys at 147'" said Richard Schaefer, referring to either Manny Pacquiao or Floyd Mayweather Jr.
Judah, who appeared to have trouble getting his punches off, said he thought the referee was giving him a standing 8-count to allow him to recover from a low blow and was confused when the fight was stopped.
Judah (41-7) came into the ring with a piece of the 140-pound title, but looked every bit his age of 33 in a fight he was never really in. Judah fought defensively most of the way, and when he tried to trade with Khan usually came out on the losing end.
Ringside punch stats reflected Khan's dominance, showing the British fighter landing 61 of 284 punches to 20 of 115 for Judah.
Khan, whose only loss came in a first-round knockout three years ago, was expected to have a tougher time against Judah, who has been fighting for 15 years. The southpaw, though, complained of a head butt in the first round and was hesitant to get in exchanges with a younger fighter who had better hand speed and more power.
