America's Steve Luevano sent Nicky Cook to the canvas five times on the way to claiming the vacant WBO featherweight crown at London's 02 Arena.
Luevano floored Cook early but the Briton kept battling
Dagenham's Cook, 27, was floored in the second and third rounds and twice in the ninth before being knocked out with another vicious body shot in the 11th.
It was a courageous display from Cook, who never got to grips with Luevano's southpaw, counter-punching style.
The 26-year-old Luevano's record now reads 33 wins in 34 contests.
The fight got off to a nervy opening amid a flurry of missed punches but Luevano sent Cook tumbling in the second round with a left hook.
Luevano tried to press home the advantage when the count was completed, firing a straight left from his southpaw stance but Cook recovered before finishing the round with some solid body shots.
He had never fought anyone like me before and I was able to catch him with a variety of shots
Another crisp hook had Cook reeling in the third and his problems deepened in the fourth when he staggered after receiving another stiff straight left.
A fiery exchange in the sixth brought Cook's fans to their feet and Luevano was rocked by a left hook after being pinned in the corner.
With Luevano lacking the sharpness of earlier rounds, Cook's fans were becoming hopeful their man could perhaps steal a decision.
But he was back on the canvas in the ninth when two sickening body punches - a pair of identical left hooks - twice sent him sprawling.
Refusing to be beaten, Cook took the knockdowns as his queue to start unloading on Luevano and some more ferocious exchanges ensued.
But the American's body punching was taking a terrible toll and the decisive shot was delivered in the 11th, another hook to the ribs that saw Cook counted out 30 seconds into the round.
Cook, a former British, Commonwealth and European champion, had never before been floored and was unbeaten in 27 encounters coming into the fight.
"He had never fought anyone like me before and I was able to catch him with a variety of shots," said Luevano.
"This sets me up for the big fights now. I've come a long way from home, and I'm bringing the title home."