Thirteen-year-old Lydia Ko survived a two-hole playoff against her rival and close friend Cecilia Cho to win the Australian women's golf strokeplay championship in Melbourne today.

In a New Zealand 1-2, Ko claimed the trophy after making a tap-in birdie on the second playoff hole while Cho three-putted from long range at Melbourne's Huntingdale Golf Club after both players finished on six-under par.

Cho, the defending champion, made a birdie at the 17th to give her a share of the lead for the first time.

She was forced to make an excellent up-and-down from behind the green at the last to force the playoff.

Cho, the world No 1 amateur, narrowly missed a 10m birdie putt on the first playoff hole while Ko saw her 3m birdie slip past.

However Ko, the world No 4, made no mistake with her birdie when they replayed the par-5 18th for the second time, hitting her second to within five metres.

The North Harbour player becomes the youngest winner of the Australian strokeplay and the fourth New Zealander to claim the title following Lynnette Brooky in 1993, Sarah Nicholson in 2006 and Cho last year.

She rates the victory among her best in her short but stunning amateur career.

"Yes it's right up there with being top amateur at the professional tournaments," Ko said.

"It's the first four-round win overseas so it's pretty exciting.

"I was quite nervous at times today. But I played the final hole really well in the playoff and it was good to get the win. The only thing was beating Cecilia because she is a good player and we are such good friends.

"I did not play well at (last week's) Queen Sirikit Cup and wanted to do better here. I am quite proud of myself for what I have achieved."

Ko said she has battled a stomach bug this week and felt awful during today's final round.

"I've been throwing up this week and not feeling the best. I hope that I will come right. May be the win will help me feel better. I want to do well in the amateur matchplay now and hopefully I can meet Cecilia in the final."

Ko missed a short putt to force a playoff at the recent New South Wales Open and did the same against Cho in the crucial final match of the 2010 Interprovincials.

Her coach Guy Wilson, who was on her bag this week, said the manner of the win was a sign of the maturing of his super-talented young charge.

"I guess we tend to forget that Lydia is 13. But the way she handled herself and how she played in the playoff was a big step for her. She will learn now how to go about winning four-round tournaments.

"She has worked very hard and her game is really developing well. Hopefully she can recover from this illness, because it's quite an arduous time with two rounds each day now with matchplay."

The pair dominated today, finishing seven shots clear of third-placed Minjee Lee from Western Australia.

Ko began with a two shot advantage which Cho had reduced to one shot after 12 holes.

Ko made a splendid eagle on the par-5 14th but gave up that buffer with back-to-back bogies. Cho's birdie on the 17th tied things up before the playoff decided in Ko's favour.

Cho shot the day's low-round of three under par 70 while Ko managed a one-under 72.

They will be the only New Zealanders to make the matchplay with North Harbour's Faye-Amy Nickson shooting a one-over 74 to finish in a share of 46th place and Waikato's Emily Perry finished in 54th place.

Leading scores, round 4, Australian women's amateur strokeplay, Huntingdale GC Melbourne, par 73:

286 Lydia Ko (NZ) 70 73 71 72, Cecilia Cho (NZ) 70 77 69 70
293 Minjee Lee (Australia) 77 67 74 75
294 Yi-Chien Liu (Taiwan) 72 75 69 78
297 Su Hyun Oh (Korea) 76 76 71 74, Cathleen Santosa (NSW) 74 77 72 74.

Other New Zealanders:
323 Faye-Amy Nickson 85 80 84 74
326 Emily Perry 82 77 81 86