Third would be a terrific result for most, but Ko's body language was speaking a different language.
The 15-year-old golfing phenomenon looked gutted that she had let an opportunity slip to add to her burgeoning reputation. She still hit 80 per cent of greens in regulation, so it was the putter that let her down.
It was still a surprise to see her struggle under the pressure.
At the 14th she was tied for the lead and in the heart of the green for two, looking a decent try for birdie.
Shin, on the other hand, flew her approach way left of the green and was left with a treacherous chip just to get up and down.
In the best shot of the tournament, Shin holed her chip and, perhaps rattled by such an unexpected development, Ko three-putted.
Shin walked off with a two-shot lead and Ko never threatened again.
At the end she was clinging on to third as she also bogeyed the par-three 17th.
"I'm really happy to be there because I've had a couple of good chances at this tournament but it hasn't worked out, so finally I won here," an elated Shin said after.
Shin mixed three birdies with two bogeys in a final round dogfight with Ko and Tseng, and added the Australian title to her two British Opens among 37 professional victories.
Final round leaderboard
Jiyai Shin (Korea) -18
Yani Tseng (Taiwan) -16
Lydia Ko (NZ) am -14
Moriya Jutanugarn (Thailand)-13
Beatriz Recari (Spain) -13
Carlota Ciganda (Spain) -12
Gwladys Nocera (Italy) -12
Katherine Hull-Kirk (Australia) -11
Catriona Matthew (Scotland) -11
Thidapa Suwannapura (Thail) -11.