Klas Eriksson and Jean Hugo are knotted in second place one stroke back at 4-under-par 67 at the Val Course at Aa Saint Omer Golf Club.
David Dixon, Cedric Menut, Cesar Monasterio, Adrien Mork and Juan Parron are tied for fourth place at minus-3.
This is a joint European Tour-Challenge Tour event as the majority of European Tour stars are in New York for the U.S. Open at Winged Foot Golf Club.
The start of the opening round Thursday was delayed by almost two hours due to heavy rainfall. All players completed their opening rounds although only 29 golfers of the 154 that finished the first round broke par.
Aguilar wasted little time in breaking into red figures on Thursday with a birdie at the par-4 opening hole. He added another birdie at the fifth before surging up the leaderboard around the turn.
He birdied the eighth, ninth and 10th holes to reach 5-under par. Aguilar dropped a shot at the par-3 11th, but reclaimed the lost stroke at 15 to move into sole possession of the lead.
Aguilar turned professional 1999, but did not reach the European Tour until the Final Stage of Q School last year. He hedged his bet as he tried to make the European Tour - he founded his own construction company.
'I have a partnership in a construction company and another one that makes windows and doors,' said Aguilar. 'It's hard to find sponsors and you really have to put your hand on your own pocket. Telefonica del Sur have been supporting me for the last few years because they believe in the program that I showed them.
'I actually decided to tour professionally about five years ago. I was a professional before that, but I also had to work in my office. Then I said that I would quit my office and work towards this. I made a five-year plan, which Telefonica supported, and got my card after four years so I was very pleased with that.'
Eriksson was 2-under through 15 holes, but closed with birdies at the 16th and 18th to get into a share of second.
Hugo, who started his round on the back nine, was only 1-under par through 15 holes, but closed with three consecutive birdies to join Eriksson in second.
David Drysdale, Alessio Bruschi, Thomas Feyrsinger, Chris Gane, Simon Hurd, Henrik Nystrom, Michele Reale, Lee Slattery, Nicolas Vanhootegem and Tom Whitehouse share ninth place at 2-under-par 69.
Defending champion Joakim Backstrom struggled to a three-over-par 74 and is part of a group tied for 87th place.