Mr Osborne (52), of Christchurch, said he began playing golf after his leg was amputated 30 years ago because of cancer.
''I took it up for a bit of recreation and started to enjoy it and have been playing seriously for about five years.''
Too much of his leg was removed to allow him to use a prosthesis while hitting a golf ball, he said.
He uses crutches to walk between shots. Playing off a 16 handicap, he completed 18 holes yesterday in 91 strokes.
''I had a shocker - the greens were cored and sanded last week and were hard to putt on.
''It was hard for everyone. Even the single-handicappers were having trouble and three-putting.''
Amputee Golf NZ president Alan Dearden, of Christchurch, said 13 amputee golfers played a practice round at the club on Wednesday.
They played 18 tournament holes yesterday and were set to play a final 18 from 11am today.
The golf would be followed by a dinner and prizegiving in the course clubroom tonight.
Mr Dearden said he was amazed Mr Osborne could hit a ball standing on one leg.
''How the hell he does it, I don't know. I couldn't do it. I'm an amputee and wear a prosthesis.''
The annual tournament, in its ninth year, alternates between the North and South Islands.
Next year, the tournament will be held on Waiheke Island.
