Colin Montgomerie, joint leader overnight, dropped to seven shots off the pace in the second round of the Novotel Perrier French Open today.
Montgomerie carded a five-under-par 67 in yesterday's first round, closing with four birdies in his last five holes, the same stretch over which he finished with two eagles to win here two years ago.
That gave the seven-time European number one a share of the lead with local favourite Jean-Francois Remesy and Sweden's Marten Olander who equalled the European Tour record with eight consecutive birdies at Le Golf National.
But the 38-year-old Scot failed to take advantage of his good fortune as he carded three birdies and three bogeys - two of those on par fives - to card a level par 72.
In contrast South African Trevor Immelman was in superb form, firing eight birdies in a near-flawless round of 64, one shot off the course record, for a 12-under-par halfway total.
Remesy was his nearest challenger, some four shots adrift after adding a 69 to his opening 67, with Scotland's Andrew Coltart, Sheffield's Malcolm Mackenzie and New Zealander Stephen Scahill a further shot back.
Immelman, runner-up in the Amateur championship in 1997, missed the cut in last week's Spanish Open, but a swing fault spotted by new coach Claude Harmon - son of Tiger Woods' coach Butch - has been rectified and sparked his lowest ever round on tour.
"I've worked for years with my brother Mark but he is head coach at Columbus State University near Atlanta and I've not been able to see him enough," said Immelman, who has been compared to compatriots Ernie Els and Retief Goosen in his native South Africa ever since his successful amateur days.
"So I've started working with Claude and asked him to have a look at my swing last week and he immediately spotted that I was overswinging and needed to shorten the backswing.
"It did not quite work last week but I felt I was starting to play well and it gave me more control over the ball."
That new-found control helped Immelman to eight birdies and no bogeys, the highlight of his round coming with a seven-iron from 171 yards faded to within an inch of the hole on the testing par four 15th, where the green is almost entirely surrounded by water.
"I think that's the best shot of my career so far," added Immelman. "I'm a natural drawer of the ball so that shot is not the easiest for me to hit, so to pull it off was something special, especially when you stand over the ball and all you can see is water."
Defending champion Jose Maria Olazbal had opened with two birdies in his first three holes, although a bogey on the second - where he took a double-bogey five yesterday - left him on four under.
Des Smyth led the Irish challenge but today's 74 for a one-over total may be one shot too many to make the cut. Ronan Raffety made a notable improvement with today's 70 but at three-over after yesterday's 77 the 38-year-old will not make the cut
Philip Walton was too far off the pace at six-over after 10 holes and needs a vintage performance on the final stretch to have any chance of being around for the weekend.