The veteran Denver welterweight was working in the clinch with Che Mills in the first round when he suddenly dropped to the mat. Referee Herb Dean stepped in and waved off the bout. The time was 2:28 for what goes into the books as a TKO.
Mills, a native of Gloucester, England, controlled the bulk of the fight. Mills scored a quick takedown and spent most of the round controlling from the top. Ludwig had worked his way back to his feet when his knee gave way.
"It wasn't really a set game plan," said Mills. "I was training so hard and was ready for anything. The takedown was there, so I took it."
Ludwig (21-14) has now dropped three straight and is 2-5 in his most recent UFC stint, with all of his losses via stoppage. Mills (15-5, 1 NC), in his first fight after losing to Rory MacDonald at UFC 145, won for the sixth time in his past seven.