Bernd Wiesberger said he had to overcome a sticky start to his third round before he was able to overhaul Ross Fisher at the top of the Portugal Masters leaderboard.
The Austrian, bidding for a third victory this season, parred the first seven holes before going on a birdie spree that saw him pick up six shots between the eighth and 14th.
Fisher matched four of those but a bogey at the 18th means it is Wiesberger who leads by one entering Sunday's final round.
"After seven holes I wasn't thinking about a 65 today but that's part of the game and I knew it was tricky on the front nine," he told Sky Sports.
"I hit better shots around the turn and into the back nine, took my chances and played beautifully the back nine. It could have been a bit lower but very happy with a 65.
"Ross is a top guy so it was very relaxing out there, unfortunately he bogeyed the last but it was a very even game and I felt very comfortable."
Fisher had mixed emotions having seen a three-shot overnight lead vanish, while nursing a sprained ankle picked up at the start of Friday's round.
"Relieved, pleased, a little disappointed," he said. "To come through another 18 holes the way foot's been I'm very pleased, it would have been nice going out there tied with Berndt but it wasn't meant to be.
"Six-under today was a tremendous score so I tried to keep my neck out in front, didn't manage to do it but only one shot behind so there's still a lot to play for.
"It (the ankle) is a lot easier today, the swelling wasn't as bad as we thought it would be today so I went out there and played golf and a 69 - I'm pretty pleased with that."