Overnight leader James Heath struggled to a 73 at Aa St. Omer Golf Club to fall back into a tie for third place with Adam Groom, Raphael De Sousa, James Hepworth and Iain Pyman at 4-under-par 209.
Suneson began the day tied for 34th and parred his first five holes before he picked up the first of back-to-back birdies at the par-4 sixth. Suneson then birdied two in a row from the par-5 ninth to move to minus-3.
The Spaniard birdied the par-4 12th and added a birdie at the par-4 13th to reach 5 under. Suneson then birdied the par-5 14th to make it three in a row.
He parred his next two holes but a bogey at the par-3 17th dropped him back to minus-5. Suneson parred the last to secure a share of first.
'I putted well and was very positive,' said Suneson. 'Every week I seem to be getting up there but haven't been able to close the door, but as long as I keep knocking I think I might have a good chance of doing it. We'll see what happens.'
Fisher was on fire on the front nine with four birdies, including three in a row starting at the par-5 seventh. The Englishman found trouble on the back side, however, with back-to-back bogeys from the 11th and a double-bogey at the par-4 13th.
'I got off to a solid start and didn't really hit a bad shot on the front nine,' said Fisher. 'But you are always going to have highs and lows in the round.'
He responded well with three consecutive birdies starting at the 14th and parred his way in for a round of 68.
Heath had a quiet start with six straight pars before he lost the lead with a double-bogey at the seventh. The 22-year-old came back with birdies at the eighth and 10th holes but he stumbled to a bogey at the 12th.
The Englishman countered with a birdie at the par-5 14th to grab the lead again at 6 under but a double-bogey at the 17th left him one shot off the pace.
Gary Orr, Sion E. Bebb and Joakim Backstrom posted matching rounds of 68 to share eighth place at 3-under-par 210. Kyron Sullivan and Birgir Hafthorsson were one shot further back at 2-under-par 211.