Gallacher had raced to three under for his round after just four holes but then played his closing seven holes in five over, including putting his tee shot in the water on the 18th in a round of 73.
It dropped the Scot back into a share for fourth place at three under, tied with compatriot Scott Jamieson and defending champion Graeme McDowell and trailing behind visiting American Kevin Stadler.
Stadler, winner of this year's PGA Tour Waste Management Open, also made a mess of the last, spoiling his July 4 Independence Day celebration ever-so-slightly with a double bogey in a score of a 68 to finish on 10 under par, three clear of Frenchman Victor Riu.
"It's nice to see the US flag up there on top of the board but there's no plans to do anything special later today," he said.
"No Budweisers or anything like that. Just get ready for tomorrow's round."
Galllacher headed straight to the practice putting green for a 10-minute session before rushing back to his hotel to catch TV coverage of the France v Germany World Cup showdown.
"I just lost my rhythm a bit on the back nine and that's why I went straight to the practice green, as I missed a lot of putts on that back nine," he said.
"But if that is my worst round and to be sharing fourth then that's not too bad.
"If I can get off to a similar start tomorrow and keep it going then I'm right back into this tournament."
Jamieson is on target to lift Scotland's Open Championship contingent to eight after adding a round of 70 on his favourite course.
He arrived in the French capital having missed out on qualifying for The Open in Tuesday's qualifier at Glasgow Gailes.
However, after falling short by two strokes in making the play-off, the Glaswegian is well in the frame to pick up one of the three Royal Liverpool places available this week in Versailles.
"It was another steady day's play where I hit a lot of fairways but while I felt there was plenty of opportunities to go lower it was another under-par round," he said.
"And there's still plenty of gas in the tank for the weekend as I would not have gone to Tuesday's qualifier if I didn't think I could play all four rounds here in France.
"Besides this is my favourite golf course of the year because it is so very demanding and every part of your game has to be on, particularly off the tee.
"Then there's the spectacular finish where it's pretty cut-throat stuff so that's why I like the course so much."
Another matter of high importance to Jamieson is that this weekend marks only the eighth time all season he will play four rounds in a tournament, having missed the cut in his other eight events including those in each of the past two weeks.
Meanwhile, Aberdeen's Richie Ramsay is in doubt for next week's Scottish Open having withdrawn after 14 holes with a neck injury.
Ramsay went into the second round at five over par and was even par after nine hole, only to drop a shot at 10 and then double bogey his 12th.
He birdied the 13th but headed straight to the physio van following a par at 14 and withdrew at seven over par before seeking a courtesy car to begin his journey home. He said: "I'm not sure about my neck. All I want to do is get a car to the airport."