Gary Emerson matched Jacquelin's 64 to move into a share of second place at 11-under-par 131. He was joined there by Darren Clarke, who carded a 4-under 67.
Jose-Filipe Lima is one stroke further back at minus-10 after back-to-back 66s. Ian Garbutt also posted a 64 to end at 9-under-par 133. He was joined there by Stuart Little, who shot a 66.
Jacquelin started on the back nine at Club de Campo and quickly got into red figures with a birdie on the 11th. He kept rolling with a birdie on the 12th and another on the par-4 13th.
The Frenchman then drained his fourth straight birdie on the par-4 14th to move to minus-11. Jacquelin parred his next four holes before sinking the fifth birdie of his round at the first.
The 33-year-old stumbled to his first bogey of the event on the par-4 second, his 11th. Jacquelin got that stroke back as he birdied the par-5 fourth. He came right back to birdie No. 5 and move to 13 under.
Jacquelin, who is searching for his first tour win, birdied the par-5 seventh. He climbed to 15 under with a birdie at the eighth, but faltered to another bogey on the ninth as his lead slipped to three.
Emerson opened with a birdie on the second. The Englishman then birdied the seventh and eighth for the second straight round to get to minus-7. He parred the next three holes around the turn.
The 45-year-old then dropped in a birdie putt on the par-4 12th. Emerson birdied each of the next two holes to get to minus-10. He closed with a birdie on the par-4 16th.
Clarke birdied the second and fourth to start his round. After dropping a shot on the fifth, he ran off three straight birdies from the par-4 sixth.
The Ulsterman parred four holes in a row before dropping a shot at the par-4 13th. Clarke got that stroke back with a birdie on the 16th to share second place.
Ian Woosnam, Paul Lawrie, Damien McGrane and Graeme Storm share seventh place at 8-under-par 134.
The story of the day Friday was Ivo Giner. The Spaniard fired an 11-under 60 in preferred lies, to vault from a tie from 109th into a share of 11th. Due to the preferred lies, the 60 will not stand as the course record. Giner stands alongside David Park and first-round co-leader Mark Roe at minus-7.
'It's like a dream, I'm still shaking,' said Giner. 'The second nine was really perfect and I don't remember putting like that ever. It's like being in a cloud.'
Robert Karlsson, who shared the first-round lead with Roe, struggled to a 5-over 76. He tumbled into a share of 52nd place at 3-under-par 139.
The cut line fell at 2-under-par 140 with 75 players advancing to the weekend. Among those who missed the cut was Seve Ballesteros. Ballesteros, playing for the first time in two years, shot 77-73 to end at plus-8.