Branden Grace shot a 5-under 67 and extended his lead to five shots after the second round of the Dunhill Links Championships on Friday.
Grace credited a practice round with British Open winner and fellow South African Louis Oosthuizen for helping him improve his standing at 17 under.
Grace teed up on the Old Course, where Oosthuizen won golf's oldest major two years ago. He birdied four straight holes mid-round to add to his opening-day record score of 60 at Kingsbarns.
Joel Sjoholm of Sweden, in his first competitive round on the Old Course, matched Grace's score of 67 to move into second at 12 under, tied with Thorbjorn Olesen of Denmark (69).