New Zealand golfer Lydia Ko, 15, has advanced to the final of the US amateur women's championship in Ohio.

The world No.1 ranked amateur beat Ariya Jutanugarn of Thailand 3 and 1 in a semi-final at The Country Club course in Cleveland on Sunday NZT.

Ko will play American Jaye Marie Green, 18, who eased past Nicole Zhang, 20, of Canada, 2 up in the other semi-final.

Both players will be competing in their first USGA championship final.

Ko went 2 up with a birdie at the par-3 11th but lost the par-5 12th to Jutanugarn's birdie to see her lead shrink to 1 up. They halved the next two holes with pars.

Ko then finished with a flourish. At the par-5 16th, she hit the green in two shots and two-putted for another birdie to again go 2 up.

On the 17th Jutanugarn missed the green while Ko hit her approach shot close to the hole. She conceded Ko's birdie putt to give the New Zealander the victory.