Defending champion Joost Luiten and 2012 winner Bernd Wiesberger moved into first and second as the third round of the Lyoness Open powered by Greenfinity progressed in Austria.
Dutchman Luiten had stormed to the top of the leaderboard thanks to a front nine of 31, which moved him to ten under par.
That was enough for a two shot lead over Sweden's Mikael Lundberg and local favourite Bernd Wiesberger, who winner needed to win the title for a second time to guarantee qualification for next week's US Open Championship.
Earlier, England's David Horsey charged into contention for a third European Tour title at Diamond Country Club.
Horsey began the day in a tie for 47th place after consecutive rounds of 73, but added a sparkling 65 in the third round to surge up the leaderboard.
The 29 year old from Stockport, whose last victory came in the Trophée Hassan II in 2011, picked up a shot on the first hole and after a run of three pars, birdied the next five holes in a row to reach the turn in 30.
Another string of pars halted the former Walker Cup player's momentum, but he then birdied the 15th and 16th before dropping his only shot of the day by three-putting the 17th.
Horsey, who was 35th in the BMW PGA Championship on his last appearance, said: "With no wind, not a cloud in the sky, it was ideal scoring conditions.
"It's been coming for a while to be honest, I've been hitting it nicely on the range and just not quite been able to take it out on the golf course.
"Today I just stuck to my process a little more I suppose, went out not really thinking about anything other than myself and managed to hit a lot of good shots and hole some nice putts. I've been putting well for a while, just not been giving myself birdie putts."
Asked if the fast and firm conditions suited him, Horsey added: "Absolutely. I'm one of the shorter hitters out here and it needs to be an advantage in hitting the fairways, whether you are 30 or 40 yards back or not because if the rough is thick you can't stop it, it's hard to get it close and it makes it a bit more of an even playing field.
"It's always nice any time you get six, seven or eight under par, especially on this course the way it's playing."
At five under par Horsey was four off the lead when he signed his card, but his deficit had increased to five as the leaders reached the midway point of their rounds.
Luiten dropped his first shot since his 16th hole on Thursday when he three-putted from the back of the 14th green, cutting his lead over Wiesberger in half.
Lundberg's challenge had faltered with bogeys on the tenth and 12th, while Slattery had plummeted down the leaderboard due to bogeys on the eighth and ninth and a triple-bogey seven on the tenth, where he found the water.
Luiten bounced back immediately with a birdie on the par five 15th thanks to a brilliant approach from a fairway bunker, while Wiesberger completed a 66 in style with a birdie of his own from 20 feet on the 18th.
That briefly closed the gap to Luiten to a single shot, but the 28 year old Dutchman promptly holed from 35 feet for an unlikely birdie on the 17th to edge two clear once more.