Tony Bellew was unsuccessful in his bid to take the WBC light-heavyweight title from Canada's Adonis Stevenson in Quebec City.
Stevenson won in a sixth-round technical knockout, the first time Bellew had been stopped in his 23-fight career.
A huge left-hand knocked Bellew off his feet and, although he beat the count, the fight was stopped by referee Michael Griffin when the Liverpudlian was boxed into a corner and taking more punishment moments later.
Bellew, who lost a world title challenge to Nathan Cleverly in 2011, had boxed smartly in the early rounds and drew blood from Stevenson's nose in the third.
But Stevenson found his range with the left hand later in the third round, snapping Bellew's head back on a couple of occasions.
A wild exchange in the fourth saw Stevenson go down, but it was ruled a slip after the fighters' feet tangled.
Urged by his corner to vary his attack, Stevenson did just that in the sixth, setting up the knockdown with a right to the ribs.
"He said I'm a dwarf, and the dwarf knocked him out," said 36-year-old Stevenson, who was giving up four inches in height and five years in age to the 6ft 3in Bellew.
"I told him, when he's going to feel my power, I'm going to drop him out."
Stevenson improved his record to 23 wins - including 20 knockouts - with just the one defeat and he is now targeting a fight with England's Carl Froch or American veteran Bernard Hopkins, rather than a unification showdown with unbeaten Russian Sergey Kovalev.
"The fans of Quebec City want Carl Froch or Bernard Hopkins," said Stevenson following his victory. "Kovalev is a good fighter too.
"I don't have a problem with Kovalev, right now but the fans of Quebec City want Carl Froch and Bernard Hopkins. That's what the fans want."
Kovalev defended his WBO version of the light-heavyweight title with a second-round knockout of Ukrainian Ismayl Sillakh on the same card.
Should Tony Bellew move up to cruiserweight?