Overnight leader Kyron Sullivan struggled to a 1-over 72 to slip into a tie for second place at 4-under-par 138. He was joined there by Stephen Browne (69) and Murray Urquhart (68). Juan Abbate, Oyvind Rojahn and Simon Dyson are two strokes further back at minus-2.
Suneson, who began his round four strokes behind Sullivan, picked up a birdie at the par-3 second. After a trio of pars, the Spaniard dropped in a birdie at the par-4 sixth.
The four-time winner on the European Challenge Tour came right back with his third birdie at the seventh. Suneson climbed to minus-5 with a birdie at the ninth on the Val Course at Aa Saint Omer Golf Club.
Suneson faltered to a bogey at the 10th for the second straight round to slip back to four-under. He birdied the par-5 14th before parring his final four holes to maintain the lead.
'I took the whole year off last year and went to Sarasota (Florida) to the Leadbetter Academy,' said Suneson. 'I have always been a bit of a tense person and my swing wasn't up to scratch and I needed to make a few changes if I wanted to keep playing on tour basically. That's it really, I am playing a lot better and we'll just have to wait and see at the weekend if I can keep it going because you never know with this game.'
Sullivan notched a birdie at the fifth and a bogey at the ninth, to head to the back nine at minus-5. From there, Sullivan road a roller coaster through the back nine.
He faltered to a double bogey at the par-3 11th, but came right back with a birdie at the next. Sullivan bogeyed the 13th to fall back to 3 under.
Sullivan then birdied the 14th for the second straight day, but tripped to another bogey at the 16th. He managed to grab a share of second with a birdie on the par-3 17th.
Browne birdied the seventh and ninth to get to minus-4. He dropped a shot at the 11th, but birdied the last to end at 4 under.
'I'm a bit of a traditional Irish wind player actually, and it was really blowing hard out there over the past couple of days, but I do seem to play well in the wind,' said Browne, who resides in Dublin. 'I'm pleased with the way I have been hitting it and I only made one bogey today, which was pretty good going given the conditions.'
Urquhart parred his first six holes, then posted two bogeys and two birdies over the next four holes. He ran off three consecutive birdies from the par-4 12th to move to 4 under.
Jean-Francois Lucquin, Marc Farry and Massimo Florioli share eighth place at 1-under-par 141.
Brian Akstrup and James Hepworth each carded rounds 4-under 67 to move to even-par 142. They were joined there by 12 other players.
The cut line fell at 5-over-par 147 with 82 players moving on to the final two rounds.