Sindhu, a two-time bronze medallist at the World Championship, could not play her game and went down 17-21 21-13 11-21 to Okuhara in a women's singles match that lasted more than an hour.
The only time Sindhu faced Okuhara was in Badminton Asia Youth Under-19 Championships in 2012 and the Indian had beaten the Japanese then in a close three-game match but she couldn't do it this time.
Sindhu was no match for her rival in the opening game as Okuhara led throughout after reeling off eight straight points at 4-3. Sindhu narrowed the gap to 17-19 but the Japanese soon pocketed the game without much ado.
The decider begun on a competitive note as both the shuttlers fought hard for each point and moved neck and neck with Sindhu managing a one-point lead at the interval. But she crumbled after the breather as Okuhara registered 11 points on a trot to bang the door on the Indian.