The fight took only 51 seconds from start to finish.
After a quick feeling-out process, Nelson uncorked an overhand right that landed perfectly on Herman's chin. Herman went down in a heap. Nelson followed up with one punch to his fallen opponent, but ref Steve Mazzagatti was already stepping in to call a finish to the fight.
Herman protested the stoppage, but it was clear from his body going limp as he went down that he was out at least momentarily.
The knockout was reminiscent of Nelson's KO of Stefan Struve in March 2010. It was his second win in three fights as he improved to 17-7.
Herman, who took the fight on short notice, replacing Gabriel Gonzaga, fell to 21-4. After beating John Olav Einemo in his first UFC fight, he's lost two straight in the octagon.