Marcel Siem carded a 3-under 69 on Saturday to hang on to the top spot at the Trophee Hassan II.
Siem, who has led at the conclusion of each of the first three rounds, finished 54 holes at Golf du Palais Royal at 15-under-par 201.
If he is able to capture his third career victory on the European Tour, he has a chance of earning an invitation to the Masters.
"It is very nice to have the gap back for the start of the final round tomorrow," said Siem. "I am pretty confident at the moment, so I know the swing is there when I trust it and just let it go. That will be very important tomorrow."
2011 winner David Horsey (70), Mike Ilonen (70) and Pablo Larrazabal (69) shared third at 11-under, while Bernd Wiesberger (69) sat in fifth at 9-under.
Craig Lee (70) occupied sixth place at minus-8.
Siem opened the day with a 3-stroke lead over Ilonen and Horsey, but a bogey at the first coupled with Ilonen's birdie at the third dropped his advantage to just a stroke.
Horsey, meanwhile, recorded birdies at the first and sixth around a bogey at the third to join Ilonen a shot off the pace at 10-under.
After Siem and Ilonen each birdied the seventh and Horsey birdied the eighth to keep it a 1-stroke difference, Horsey poured in his second straight birdie at the ninth to join Siem atop the leaderboard.
Ilonen countered his birdie with a bogey at the eighth to fall two back from the leaders.
Siem, however, regained the outright lead for good with back-to-back birdies at the ninth and 10th, moving him to 14-under.
Another birdie at the 12th separated him further from the field, as Horsey followed three straight pars from the 10th with a bogey at the 13th to fall to minus-11.
Ilonen's eagle at the 10th put him alone in second, but his bogey at the 13th dropped him back into a tie with Horsey.
Ilonen then traded a birdies at the 15th and 17th with bogeys at the 16th and 18th to stay at 11-under.
"I am four back and would rather be a little bit closer, but we have three guys four behind that can catch him but one of us will have to go really low tomorrow and I think the golf course will allow that," Ilonen said. "I have made enough birdies and eagles to know I can do it, but I just have to avoid the mistakes."
Horsey also briefly grabbed sole possession of second place with a birdie at the 17th, but he closed with a bogey at the last to fall back even with Ilonen.
Siem ended his round by nullifying a birdie at the 16th with a bogey at the 17th to stay at 15-under.
"I had to hole a few big putts just to stay ahead and then I managed to pull away a little bit," said Siem. "But then 15 and 17 were disappointing because you are really looking to pick up a couple of shots there but I managed to give one away."
Larrazabal had a birdie and eight pars through his front nine before trading four birdies with a pair of bogeys over his last nine holes to grab a share of second place.
NOTES: Siem is seeking his first trip to the Masters ... Emiliano Grillo hit a hole-in-one at the 15th hole ... 2012 champion Michael Hoey struggled to his second 2-over 74 in three rounds to fall into a tie for 39th place at 1-over- par 217 ... Horsey, Ilonen and Larrazabal are also trying for their third win on the European Tour.