Derksen, who shared the lead with Jean-Francois Lucquin when the second round was completed Saturday morning, stood at 10 under par through 15 holes of his third round.
Gregory Bourdy was in the clubhouse at 9-under 201 following a 64 at Pula Golf Club. He was one of the 53 players who was able to finish the third round.
Lucquin fell one shot off Derksen's pace and was at 9 under par through 15 holes.
Peter Lawrie and Sam Little were both on the course at 8 under, while Richard Finch (66) held the second-best score in the clubhouse at 7-under 203.
Alexander Noren (64) stood at 6-under 204, and 2004 Mallorca Classic winner Sergio Garcia was 5 under through 17 holes when play was stopped.
The man who beat Garcia last year, Niclas Fasth, tumbled from contention when he played a stretch of five holes in the middle of his round at 7 over par.
The defending champion made four bogeys and a triple-bogey on holes 9-13 and fell from a tie for sixth place after the second round into a tie for 53rd place at plus-3. Fasth was through 15 holes.
Derksen played the front nine at even-par, making a bogey at the third hole and a birdie at the seventh. He posted back-to-back birdies from the 10th, then made another bogey at the 12th.
He avoided a third bogey by getting up-and-down from the sand to save par at the 13th, then posted a pair of pars to remain in the lead.
Derksen is seeking his third European Tour win and first since 2005.
Lucquin, looking for his first victory, had two birdies and a bogey on the front nine. He made another bogey at the 12th, then a birdie at the 14th that gave him a share of the lead again with Derksen.
But Lucquin couldn't avoid a bogey at the 15th before the horn sounded.
Eighteen players were still on the course when the round was suspended. The tournament hasn't been able to get back on track after a long weather delay in the first round on Thursday.