Argentina's Eduardo Romero collected seven birdies and one bogey for a 66. He suffered his lone mistake on the 18th hole and dropped into a share of second place at eight-under 136 with defending champion Jose Maria Olazabal (67) and Jean-Francois Remesy (69).
Immelman posted eight birdies Friday, four over his last five holes. He knocked a seven-iron stiff from 170 yards out at the island green 15th, tapping in for birdie to break into double-digits under par.
'I would rank that as the best shot I have hit in my career so far,' he said. 'It was a knock-down fade seven-iron. I naturally draw the ball so it was a shot that is not the easiest for me to play so when I pulled it off it was something special.
'The 15th is surrounded by water and the pin is cut tight. You are standing over it and all you see is water. To pull that shot off gave me a lot of confidence.'
After adding a birdie at the 17th, Immelman hit his second shot to 15 feet at the par-five closing hole then just missed the eagle attempt that would have tied the course record.
Instead he settled for another birdie and a 64, the best round of his short career on the European Tour.
Immelman shot 65 three times in 2001, his first full season on the European Tour. A victory at the Tusker Kenya Open on the 2000 Challenge Tour helped earn him a spot in the big leagues in '01, and he also captured the 2000 Vodacom Players Championship on the Southern Africa Tour.
Although Immelman won the South African Amateur Championship in 1997, that same year he lost in three other amateur finals: the British Amateur at Royal St. George's, the New Zealand Amateur, and the U.S. Junior at Aronimink.
A year later he won the U.S. Amateur Public Links Championship at Torrey Pines in Southern California.
Immelman has begun working with Claude Harmon, son of Butch Harmon, who coaches Tiger Woods and a number of other big-name players. The younger Harmon has tried to correct his student's tendency to overswing, and the result has brought more consistency to Immelman's game.
Immelman hopes to soon take his place among the growing list of young guns who have taken the golf world by storm in recent years.
'You have Adam Scott, Justin Rose and Nick Dougherty playing well and Charlie Howell and all the guys in the States, Luke Donald, Paul Casey, the list goes on forever, not forgetting Sergio [Garcia] who is top-five in the world,' Immelman said. 'Over the span of my career those are the guys I am going to be playing against over the next 10 or 15 years.'
New Zealand's Stephen Scahill (65), Scotland's Andrew Coltart (66) and Malcolm Mackenzie (69) of England were together at seven-under par, one shot ahead of Englishman Gary Evans (67) and Swedes Carl Pettersson (68) and Marten Olander (71).
Colin Montgomerie, who won the Open de France the last time it was contested at Le Golf National in 2000, shot an even-par 72 Friday. He was part of a five-way tie for 11th at minus-five.
Friday's play was suspended for one hour and 25 minutes due to torrential rain.