Adonis Stevenson stopped Chad Dawson with a single, swinging left-handed punch at 1:16 of the first round on Saturday to capture Dawson's World Boxing Council light heavyweight world title.
Stevenson, a Haitian-born Canadian who at 35 has fought just 22 professional fights, improved to 21-1 with 19 wins inside the distance.
Dawson, who was trying to bounce back from a 10th-round loss to Andre Ward in a fight in which Dawson stepped down to super middleweight, instead suffered an even more embarrassing defeat, falling to 31-3.
Dawson was winding up to throw a right when southpaw Stevenson nailed him on the side of the head. When he rose, his eyes were glazed and his legs wobbly and the referee called it off for the technical knockout.