'I started off very nicely. Felt very comfortable and in the middle of the round I hit a few funny shots,' said Tunnicliff. 'It was really up and down, really a roller coaster today.'
Anders Hansen fired an 8-under 64 early at the PGA Centenary course to move from a tie for 34th into a tie for second. Hansen was joined by Nick O'Hern and Santiago Luna at 6-under-par 210.
Tunnicliff, who battled the wind on Friday to open a five-stroke edge heading into the weekend, was greeted by optimal scoring conditions under sunny Scottish skies but was unable to take full advantage.
'I would have preferred a bit more wind like the first two days,' said Tunnicliff, who is seeking his first win since the 2002 Great North Open. 'I just tried to go and play my game.'
The Englishman reached the par-5 second in two for an early birdie to move to 10 under but he found trouble with the first of back-to-back bogeys at the par-4 fifth.
At the par-3 10th, Tunnicliff knocked his tee shot inside 6 feet and drained the birdie try to stand three clear of the field. While O'Hern applied the pressure, Tunnicliff persisted and remained ahead by three thanks to a birdie at the 12th.
Tunnicliff hit a bad drive that went into a bush at the par-4 12th and was forced to take a penalty drop into the rough. He had a look at the green, however, and sent his second shot to 8 feet.
He was unable to convert for par and another dropped shot at the 14th saw his one commanding lead shrink to a single stroke. Tunnicliff recovered quickly, however, and ran home a 13-foot putt for a birdie at the par-4 15th.
Tunnicliff then landed his second shot on the green at the par-5 16th and took two putts for another birdie to return to minus-10. Tunnicliff wasn't out of the woods though and faltered with a bogey at the very next hole.
'I'm playing pretty solid,' said Tunnicliff. 'All in all, I'm pretty confident in my swing.'
Hansen parred his first six holes before catching fire down the stretch. The Dane tallied back-to-back birdies from the seventh and added a birdie at the par-4 11th to reach 1 under.
The 33-year-old then eagled the par-5 12th and closed with three birdies over his last four holes to for his share of second.
O'Hern, who held a share of the opening-round lead with Tunnicliff, had a rocky front nine with three birdies and three bogeys.
The left-hander made a run on the back side, however, with three consecutive birdies starting at the par-4 11th. O'Hern had a chance to make it four in a row but his 5-foot birdie try at the 14th skimmed the cup. O'Hern then stumbled home with a bogey at the 17th for a round of 70.
Defending champion Soren Kjeldsen moved within four of the lead with a round of 67. He was joined by Gary Evans and Russell Claydon at 5-under-par 211. Mark Roe, Raymond Russell, Henrik Stenson and Henrik Nystrom were one shot further back at 4-under-par 212.