The Dane, whose first-round 64 put him in a commanding position, has now gone four under two rounds in a row and leads Rikard Karlberg, who moved into contention with a six-under 66 that included four birdies in his final six holes.
Olesen is at 16 under and Karlberg at 13.
Benjamin Herbert matched Olesen's first-round 64 with nine birdies and a bogey. He lies third at 12-under overall, alongside Bernd Wiesberger (67), Richard Bland (68) and Thomas Levet (69).
Friday’s third round was the first not to be affected by adverse weather conditions. The first round was completed on Thursday, with part of the second round also played early on Friday after more rain.