World No 1 amateur Lydia Ko has withdrawn from the Riversdale Cup with illness after taking the round-one lead in Melbourne. The 14-year-old, who shot a three under par 70 to lead round one of the Riversdale Cup by two shots from fellow New Zealand representative Emily Perry and Australian Lauren Hibbert (both 72), woke up this morning feeling dizzy and nauseous. She withdrew from the tournament to be checked out by a doctor who will further assess her plans to play in a professional event next week in China. The North Harbour player, who was obviously tired after finishing tied 17th last week at the ISPS Handa NZ Women\'s Open hosted by Christchurch, had bounced back well in the amateur event she finished runner up last year. Ko made two bogeys and five birdies in her round to show her ability once again among her amateur peers. Ko has enjoyed a stellar season in Australia this year. She was the youngest winner of the Australian Amateur title on record before she became the youngest winner of a pro event when she claimed the NSW Open. Perry, who held a share of the first round lead last week at the Pegasus Golf Club with a five under par 67, also backed up in superb fashion. The 21-year-old from the Lochiel Golf Club in the Waikato made two bogeys and three birdies in her one under par 72 to be in a share of second place. Fellow Waikato rep Chantelle Cassidy had a four over par 77 and Sarah Bradley had a disappointing seven over 80 to be off the pace.