'I have been very relaxed these two days,' said Tunnicliff. 'I feel pretty confident especially if I can carry on the way I've been playing.'
Graeme McDowell posted a 71 to finish alongside Nick O'Hern at 4-under-par 140. Paul McGinley, Henrik Stenson and David Howell followed at 3-under-par 141.
A fierce storm battered the PGA Centenary course on Thursday halting play for nearly three hours and ultimately forcing the suspension of the first round. The conditions remained difficult for the second round, but the absence of any additional storms let play go on as scheduled.
Tunnicliff, who held a share of the opening-round lead with O'Hern, started on the 10th and stumbled out of the gate with a bogey. The Englishman wasn't the only one struggling, however, and Tunnicliff regained the lead with a birdie at the 12th under windy conditions.
He added a birdie at the par-3 14th and played his approach to the fringe 8 feet from the cup at the par-4 15th. Tunnicliff drained the birdie try but gave that shot back with a bogey at the 17th.
Tunnicliff, who earned his first career victory on the European Tour at The Great North Open two years ago following the death of his mother, rebounded on the front nine with back-to-back birdies starting at the par-5 second.
'Someone was looking down on me that week and I hope she is looking down on me again this weekend,' said Tunnicliff.
While the remainder of the field was unable to make any serious advances, Tunnicliff cruised down the stretch and added a birdie at the par-4 eighth to take a comfortable lead into the weekend.
McDowell also played the back side first and tallied two bogeys and two birdies over his first six holes. At the par-5 18th, McDowell ran home a 30-footer for a birdie but found trouble with double bogey at the first.
The 24-year-old, who won this year's Italian Open, chipped his third shot to 3 feet for a birdie at the par-5 second and knocked his approach inside 12 feet at the par-4 fifth.
McDowell converted the birdie putt and parred his way in for a share of second.
'It is nice to remember how to play in the wind again,' said McDowell.
Gary Evans, Raymond Russell, Terry Price, Peter Baker and Russell Claydon share seventh place at 2-under-par 142. Mark Roe, Santiago Luna, Paul Eales, Gary Emerson and Richard Green were one shot further back at 1-under-par 143.
Defending champion Soren Kjeldsen shot a 2-under 70 to finish in a group at even-par 144 that includes Colin Montgomerie.
The 36-hole cut fell at 4-over-par 148 with 76 players surviving for the weekend. Among those who failed to qualify were Paul Lawrie and Nick Dougherty.