The 42 year old, who won the last of his two European Tour titles in 2014, carded four birdies and four bogeys on Saturday to head into the final round on nine under par.
Aguilar held a three stroke advantage as he stood at the 18th tee but he dropped a shot at the last to slip back to where he began the day.
Home favourite Sepp Straka, Swede Johan Carlsson and South African Dylan Frittelli were the Chilean’s nearest challengers on seven under.
Aguilar started brightly, tapping in his close-range birdie putt at the first to get to ten under par.
But with playing partner Graeme Storm also picking up a shot at the first, Aguilar’s lead was reduced to one shot when he carded his first bogey of the day at the second.
He fired a birdie at the fourth – for the third day in succession – to get back into double figures, and with Storm missing his par putt at the same hole, Aguilar found himself three shots clear.
Aguilar made another gain at the seventh to open up a four-shot lead, only to drop a shot at the next.
The Chilean’s lead was back down to one when he missed a par putt at the short 14th, with Straka making back-to-back gains at the 15th and 16th to get to eight under.
Aguilar bounced back with a close-range birdie at the 15th and when Straka carded a bogey at the 17th, the gap was back to three shots.
But Aguilar dropped his fourth shot of the day after he was unable to sink his tricky par putt at the 18th.
“Today I think I left many shots on the golf course” said Aguilar after his round.
“I played quite well and I missed a couple of greens, which is normal, and several putts I missed for birdie, so it could have been a little bit better but I’m still in contention and this is what I wanted on Thursday so we will see what happens.
“I think on the greens I left a couple of shots out there that could have made a huge difference for tomorrow and hopefully tomorrow they will go in.”
Austrian Straka, who started the day four shots behind halfway leader Aguilar, reached the turn in 34 after carding three birdies and a solitary bogey on his front nine.
He fell back to six under after dropping another shot at the 11th but he recovered in style, reeling off consecutive birdies at the 15th and 16th to get within one shot of the lead.
But another bogey at the 17th saw him drop into a tie for second.
Frittelli, meanwhile, carded his only bogey at the second before making gains at the fourth, tenth, 11th, 15th and 17th to surge into contention.
Carlsson mixed three birdies with two bogeys to sign for a second successive 71.