Sweden's world No 2 Henrik Stenson shared the lead after going one better with the best round of the day to move to 13-under overall and lead the way with England's world No 346 Eddie Pepperell, who also shot a 65.
The home favourite racked up seven birdies and an eagle two at the seventh alongside one bogey to put himself in pole position ahead of the final day. Pepperell, 23, whose only professional victory came on the Challenge Tour two years ago, fired eight birdies and looked set to finish the day with the outright lead, only for a bogey at the 17th to drop him back.
Gallacher picked up eight birdies and a bogey to share third place with Spain's Alvaro Quiros who went round in 66, and the West Lothian man was pleased to be in among the final-day contenders.
He said: "That was my goal at the start of the day. I played the back nine lovely and gave myself plenty of chances. One back is not a bad place to be, but there are some tough holes out there. If you hit a loose shot you can have high numbers. You have always got to be in control."
France's Victor Dubuisson and Welshman Bradley Dredge were also well-placed on 11 under and 10 under respectively, while Chris Doak was tied 10th after a 69 left him five shots off the lead.
Pepperell was delighted with his day. "I had great fun," he said. "I felt comfortable out there. It was a great start with three birdies in a row.
"I was flying and I missed good opportunities on four and five. Then I had a sticky spell with my swing, but hung in there. I would like to have finished with a birdie from the last two holes, but I'm not too unhappy about that.
"Henrik is tied with me so it is going to be a great day tomorrow, but just have to keep focused on my game and do what I've been doing. If I do that I'll have a shot come the last and I'll enjoy it.
"Henrik is one of the best players in the world, he's in fine form and it is his home country. I couldn't ask for much more really from a final round. It's going to be really exciting for me."
On his eagle at the seventh, Stenson said: "I knew it was going to be inside 10 feet when I hit it and it landed about five feet away, had a little release and hop and went in."
The Swede added: "The crowds have been great. I haven't played in front of home crowds for a while and with the success I've had I really feel the support. I'm going to enjoy tomorrow and try to be up there with nine to go and try to win this tournament for them.
"It would be great to do it. I've not won in Sweden before and obviously I would like to do that in my career.
"It seems like I'm going to have a chance, but there is a long way to go and a lot of good players up there.
"I need to stick to my play and be there when it really matters."
More golf in digest - Page 19