Higgins had to wait 25 hours between the end of his second round and the start of his final round due to a six-hour play suspension on Friday, but by the time round two was finished on Saturday morning his co-lead stretched out to a three-shot solo lead and the only man to be under-par at -1.
After biblical conditions on Friday with a six-hour weather suspension the second round was completed before a 1.30pm shotgun start for the final round on Saturday.
Higgins had a sluggish start, dropping a shot on the par-5 1st before bogeying the short par-4 4th after almost losing his approach to the green.
But in true champions fashion, the 50-year-old managed to spread himself from the chasing pack once again with back-to-back birdies on the sixth and seventh to move three clear once more.
Higgins moved four clear with birdies on the tenth and thirteenth before Thornton saw a birdie effort stop a hair short of the hole on the 18th before he tapped in for the winning 8.
Thornton put on a late charge with birdies on 13 and 15 as he posted the low round of the day with a two-under 70 for a one-over total. Richard O’Donovan was fourth on plus five after a 75 while defending champion McGrane was a shot further back in fifth after a 71.