Suneson, who was one of three second-round leaders, completed 54 holes at 6-under-par 207.
The third round was completed despite gusting wind and occasional heavy rain.
Marcus Higley, who shared the second-round lead with Suneson and Peter Fowler, managed an even-par 71 to finish alone in second place at minus-5.
Meanwhile, Fowler struggled to a 3 over par back nine to shoot 1-over 72. He was joined in third at 4-under-par 209 by Mikael Lundberg (71). Stuart Davis and Francois Calmels are one stroke further back at minus-3.
Suneson and Higley either shared the lead or were alone atop the leaderboard throughout the third round. Suneson moved one ahead with a birdie on the first. He parred nine straight to remain at 6 under.
Higley opened with five consecutive pars. The Englishman then dropped in back-to-back birdies from the sixth to move atop the leaderboard at minus-7.
Fowler birdied the eighth and ninth on the Val Course at Aa Saint Omer Golf Club to remain in the mix at 7 under, but trouble loomed around the turn. Bogeys at 10, 14 and 16 dropped the Australian down the leaderboard.
Higley birdied No. 9 for a brief two-stroke lead over Suneson. However, Higley dropped a shot at the 10th and Suneson birdied the 11th to forge a tie at minus-7.
After bogeys on 12 and 14, Higley was two back at 5 under.
Suneson ran off five straight pars from the 12th to remain at 7 under.
Higley got one stroke back with a birdie on 16. He slipped two back with a bogey at the 16th.
Suneson faltered to a bogey at 17 to end one clear at minus-6.
'I had a good short game to keep things going and it went well today,' said Suneson. 'It was a good day and as Tiger (Woods) and the big guys all say, I have done what you need to do and that is give myself a chance to win.'
Michael Lorenzo-Vera is alone in seventh at 2-under-par 211 after an even-par 71 Saturday. Gustavo Rojas fired the low round of the day with his 4-under 67. He was joined in a share of eighth at minus-1 by Steven Alker, Gareth Paddison and Manuel Merizalde.