Siem, shot a 3-under 69 Saturday to take a four-shot lead after 54 holes at the Golf du Palais Royal links in Agadir.
Siem, who led by three shots Friday, was poised to win his third career European Tour victory Sunday. He shot five birdies Saturday but bogeyed the first and 17th holes.
A three-way tie for second place included Pablo Larrazabal, Mike Ilonen and 2011 tournament winner David Horsey.
UPI Sports Results for September 20, 2014
UPI Sports Results for September 19, 2014