Oosthuizen, with a second round of 64, moved one clear over opening round leader Thongchai Jaidee and Scotland's Scott Jamieson.
That trio have broken a massive six shots clear of a large group in a share of 4th position.
Three of the pre tournament favourites, Ernie Els, Nicolas Colsaerts and Francesco Molinari share 10th position some eight shots from the lead of Oosthuizen.
Oosthuizen is playing his first competitive event since the Alfred Dunhill event in South Africa in December and has spent the time on his farm and playing golf with friends. His week at the Alfred Dunhill was disappointing after only just making the cut but his form prior was brilliant.
Rain delayed play early on day two but the round finished on schedule with all 33 players in the limited field completing 36 holes.