Min Woo Lee took charge of the Vic Open with an eagle at the last after overnight leader Robin Sciot-Siegrist bogeyed six holes in high winds on Saturday.
A four-under 68 moved Australian Lee onto 15 under for the tournament, giving him a three-shot lead over compatriots Marcus Fraser and Travis Smyth.
The 21-year-old's elder sister Minjee Lee is a five-time winner on the LPGA Tour and sits five shots off leader Ayean Cho in the simultaneous women's event.
"It was probably one of the best rounds I've ever played regardless of score," Min Woo Lee told the European Tour.
"I've hit it pretty solid. There were a couple of shots that were bad but that happens in 50-kilometre winds so I'm pretty happy and should be proud of the way I played."
After signing for a flawless eight-under 64 on the Creek Course and consequently a two-shot lead on Friday, Sciot-Siegrist slipped to a four-way share of fourth on Saturday as he struggled to navigate high winds in the Beach Course.
The Frenchman reached the turn in 39 and finished his round in a four-over-par 76 – a score matched by Alejandro Canizares, who led after the opening round, and former U.S. Open winner Geoff Ogilvy – to fall five shots off the pace.
Smyth got himself back into contention with three birdies in his last four holes, having dropped five shots from the eighth to the 14th, while a bogey at the 17th denied Fraser sole ownership of second position.