With Paul Broadhurst, the first-day pacesetter, taking nine at the long 18th during his second round of 75, Turner's second successive 70 gave him a one-stroke lead over the Italian Costantino Rocca.
The last of Turner's three European Tour victories was in Majorca in March. On a course which has almost as much water as grass, Turner described playing the last four holes as "like tip-toeing through a minefield with hobnail boots on".
But it was Broadhurst and Northern Ireland's Ronan Rafferty on whom Le Golf National exploded. Broadhurst was three clear standing on the 18th tee - his ninth - but hooked into the lake, missed the green with his fourth shot, then chipped back into the water. "At times this course makes you look stupid. Everybody prays to God it won't happen to them, but it has to me now," he said.
Rafferty had led at four under with five to play but then had four sixes - two of them bogeys, two of them double- bogeys - and fell to two over par. Rocca, winner two years ago, double- bogeyed the 421-yard 15th, but birdied the last two holes for a level- par 72.
That was seven shots better than Jose-Maria Olazabal, who made the cut with only two strokes to spare at four over par, and 18 better than the Swede Joakim Gronhagen, whose 90 included a 10 on the 18th.
The Norwegian Per Haugsrud, by contrast, had only the second albatross of the European season. He holed his four-iron second to the 530-yard third.
The defending champion Mark Roe, the top European in the US Open last week with joint 13th place, withdrew after nine holes with a knee injury.
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