Stenson had four birdies in the second round, but also two bogeys and a double bogey.
The Swede was in a split lead after 64 strokes in the first round, but now lost and is split sixth.
Lee Min Woo had 68 strokes in the second round and is two strokes ahead of a quartet of players.
Henrik Stenson is chasing a place in Europe's Ryder Cup team and must achieve top places in the autumn on the European Tour after a tough year.
He has also shown good form in recent weeks with a third place in the European Masters last weekend and a fourth place in the Czech Republic before that.