Eric van Rooyen of South Africa shot 67 to drop out of a tie for the lead to second at 18 under at The Renaissance Club. France's Romain Langasque (65) and Italy's Nino Bertasio (bogey-free 67) were two shots further back in a tie for third.
Former Ryder Cup star Jamie Donaldson and the English pair of Matt Wallace and Lee Slattery were part of a five-strong group on 15 under. Former British Open champion Henrik Stenson went 52 holes without a dropped shot before a double bogey on the 17th left him six shots off the lead alongside Matt Fitzpatrick and Italy's Andrea Pavan, who made the cut on the mark of 5 under and surged through the field with a flawless 62.
Former No. 1 Justin Thomas was eight shots off the pace following a 70, while Rory McIlroy was a shot further back after a 68 which included four birdies in five holes from the fifth but also three bogeys.
Wiesberger turned in 31 after four birdies and was at 20 under when he dropped his only shot of the day, missing a short putt on the 17th. He recovered with his seventh birdie. He won his fifth European Tour title in May at the Made in Denmark, and the Austrian was runner-up at the Irish Open last weekend.
Three places are also up for grabs for the British Open next week at Royal Portrush, where Donaldson won his first European Tour title in the 2012 Irish Open. "I'll be keeping an eye on the leaderboard, I really want that Open spot of course, but winning is more important than that, that's the primary goal," Donaldson said. "I just need to go out there and play like I played today and then I'll be buzzing."
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