'I was so pleased today the way I played,' said Tunnicliff, who earned his maiden title two years ago at The Great North Open. 'I was just so focused all day long.'
Graeme McDowell shot a 67 to take second place at 8-under-par 280. Nick O'Hern and Steven O'Hara were one shot further back at 7-under-par 281.
Tunnicliff avoided a fierce storm on Thursday by grabbing a share of the clubhouse lead early on and opened a five-stroke edge under windy conditions. On Saturday, when the sun was shining on the PGA Centenary course, Tunnicliff could not break par, but the clouds returned for the final round and the Englishman comfortably cruised to the title.
'I was swinging really good,' said Tunnicliff. 'Played great in the wind.'
The 35-year-old vaulted out of the gate at the opening hole and sent his approach shot to the par-4 within 2 feet of the cup for a tap-in birdie. Tunnicliff then chipped his third to 5 feet for a birdie at the par-5 second to quickly move to 11 under.
'I was a little nervous in the beginning,' said Tunnicliff. 'But I started great with two birdies.'
Tunnicliff added a birdie at the ninth and two-putted for a birdie at the par-5 12th to open a six-shot lead. Tunnicliff then parred his way in with some solid saves and glanced at the leaderboard on the 18th green before he clinched the title.
McDowell provided the only challenge for Tunnicliff but the closest he got to the lead was three strokes. McDowell began an incredible birdie run around the turn starting at the par-4 eighth and converted a 6-foot putt for a birdie at the ninth.
At the par-3 10th, McDowell knocked his tee shot to 10 feet and drained the putt. He then birdied the 11th and the 12th to make it five straight.
The 24-year-old moved to 9 under with a birdie at the 15th but could not get out of a greenside bunker at the par-5 16th en route to a double bogey. McDowell responded with a birdie at the last.
Andrew Oldcorn carded a 67 to join David Lynn in a tie for fifth at 6-under-par 282. Russell Claydon, Raymond Russell and Paul McGinley followed at 5-under-par 283.
Richard Green, Gary Murphy, Stephen Gallacher, Anthony Wall and Peter O'Malley shared 10th place at 4-under-par 284.