Huck KOs Arslan to defend cruiserweight belt
German WBO cruiserweight champion Marco Huck poses during the official weighing in, in Stuttgart, Germany, on January 24, 2014 - by Sebastian Kahnert
The 29-year-old Huck put the challenger down twice in the sixth round with a furious onslaught of punches, but both times the 43-year-old struggled back to his feet.
Referee Mark Nelson stepped in to put Arslan out of his misery with 1 minute, 56 seconds of the round remaining.
"I want to thank Arslan for a really hard fight, respect to the guy who is in such good shape at the age of 43," said Huck.
Having already controversially beaten Germany's Arslan on points on their previous November 2012 meeting, Huck took control of the fight from the fourth round onwards.
This was the 26th knock-out and 37th win of Huck's career and the 12th defence of the title he won in 2009.
Arslan, a former WBA cruiserweight world champion, suffered the eighth defeat of his career but immediately ruled out retirement.
Huck has said he now wants to become a world heavyweight champion, having already lost to Russia's Alexander Povetkin at the heavier division in February 2012.
On the Huck-Arslan undercard, Britain's David Price enjoyed a first-round knockout of Istvan Ruzsinszky.
Liverpool heavyweight Price, 30, is rebuilding after back-to-back defeats by American Tony Thompson in 2013.
Hungary's Ruzsinszky was a late replacement for Kazakhstan's Konstantin Airich, who failed a medical.