David Haye returned after a three-and-half-year lay-off with a first-round knockout of Mark de Mori in London.
Australian De Mori looked bothered by the first jab Haye threw and thereafter it was one-way traffic.
Haye, 35, set up the finish with huge overhand right and De Mori was unconscious before he hit the canvas with 55 seconds left in the round.
Haye’s stated ambition is to regain the world heavyweight crown he lost to Wladimir Klitschko in 2011.
Haye’s last fight was a fifth-round knockout of Dereck Chisora in July 2012 and prior to Saturday he had fought only four times in five years.
He announced his retirement in 2013, having been advised not to fight again after undergoing extensive shoulder surgery.