South Africa's Roger Wessels posted his second straight round of 69 to finish alone in third at six-under-par 138. Andrew Oldcorn, Paul Casey, Jon Bevan and Bradley Dredge were tied for fourth at five-under-par 139.
Struver used a lucky bounce on the final hole to grab sole possession of first place. The German missed the green with his second shot but his ball bounced off a mound and landed on the putting surface. Struver ran home the 10-foot birdie putt that remained to finish at minus-eight.
While Struver played a remarkable, bogey-free round at De Vere Slaley Hall Golf Club, his halfway lead could also be attributed to a late-round collapse by Dredge.
Dredge recovered from a double-bogey on the closing hole Thursday with a phenomenal start to Friday's round. The Welshman drained three consecutive birdies after teeing off on the 10th then added another at the par-four 15th to quickly reach eight-under.
The 28-year-old faltered with a bogey at the first but recovered with a birdie at the fourth to remain perched atop the leaderboard until all fell apart at the par-four seventh.
Dredge found a greenside bunker with his approach and failed to get up and down for a bogey. His trouble continued at the following hole where he had to scramble to save bogey.
At the par-five ninth, Dredge missed his par save by mere inches. He tapped in for his fourth bogey of the day to finish three shots off the lead.
Struver, who also started on the back side Friday, had an equally strong start with a birdie at the first. At the par-four 13th, Struver made the first of four consecutive birdies to reach minus-six.
The 34-year-old collected another birdie at the third before finishing with a birdie at the closing hole.
'I haven't practiced much in the last couple of weeks,' said Struver. 'If you don't practice hard in two weeks it is hard to compete because the standard has gone up so much on the European Tour.'
Borrego, who won the Madeira Island Open in March, used two birdies over his final four holes to remain in contention.
'It was much harder in the conditions today,' said Borrego. 'It was very windy and made it very difficult to choose the right club. But I'm pleased to be where I am and I'm especially pleased with my finish, that was really good.'
Brett Rumford and Elliot Boult finished tied for eighth at four-under-par 140, while a larger group was one shot further back at three-under 141.
Defending champion Andrew Coltart carded an even-par 72 to finish nine shots off the lead at one-over-par 145.
The cut fell at three-over-par 147 with 71 players qualifying for the weekend. Among those who didn't make the grade were 20-year-old Nick Dougherty and three-time European Tour winner Mark Roe.
Full field scores from The Great North Open