Derksen and Zhang had a one-stroke advantage over Northern Irelands Ryder Cup regular Darren Clarke, who also shot a 69 in the second round of the $2.3 million jointly sanctioned European and Asian Tour event.
First-round leader Peter OMalley of Australia (74) and Englands Miles Tunnicliff (70) were another stroke back at the Tomson Shanghai Pudong Golf Club.
Derksen had five birdies and two bogeys. Zhang was the only player Friday to record a bogey-free round and holed a 25-foot birdie on the last hole to draw even.
The 42-year-old Zhang is aiming to become the first home winner of the tournament. He had previously won a European Tour event'the Singapore Masters in 2003.
Im proud of the Olympics coming up in August and Im glad to see a few Chinese players on top of the leaderboard, Zhang said. Its nice, and compared to the past, its a very exciting weekend coming up.
Im going to try my best for the gold. If I can pick up a medal on Sunday, Ill be very happy.
Derksen, winner of two European Tour events, said gusty winds made the second round challenging.
Putting has been good this week and that is a key, and if I can continue then I should have a chance Sunday, Derksen said.
Henrik Stenson of Sweden, seeking to reclaim leadership of the European Order of Merit with a good finish in this tournament, slipped down the leaderboard with a 4-over 76, leaving him five strokes off the lead along with former world No. 1 Greg Norman (73), making a rare tournament appearance.
South Africas Retief Goosen and Asian Tour leader Mark Brown of New Zealand were tied for sixth, three strokes off the pace, along with 18-year-old Chinese amateur Hu Mu.
Among the higher-ranked players to miss the cut were Spaniard Miguel Angel Jimenez, Northern Irelands Graeme McDowell and Indias Jyoti Randhawa.