Sixteen-year-old Chiara Noja broke the course record on her way to a 10-under 62 to lead the Investec South African Women's Open, with Ireland's Olivia Mehaffey well down the field after the opening round.Mehaffey carded a 79 at the Steenberg Golf Club; double-bogeys at 15 and 17 contributing to a poor day for the Belfast competitor.The German Noja, who claimed her maiden Ladies European Tour victory in Saudi Arabia in November, opened with four birdies in five holes and finished with an eagle, five more birdies and just one bogey."Over the winter I've done a lot of wedge work and a lot of the shots that I've learned to hit over this week and the start of the season I didn't have in the bag last year," she said.Noja leads by two from reigning AIG Women's Open champion Ashleigh Buhai, making only her second appearance on the Ladies European Tour after winning at Muirfield, after the South African carded a remarkable seven birdies in her first nine holes.England's Lily May Humphreys, last week's Joburg Ladies Open winner, shot a five-under 67 to sit sixth, with Scotland's Kylie Henry in a group a further stroke back. LEADERBOARD