SOUTHPORT (AFP) - Greg Norman led Padraig Harrington by a shot at the top of the British Open leaderboard with nine holes left to play at Royal Birkdale on Sunday. Defending champion Harrington had turned a two-shot overnight deficit into a two-shot lead by the sixth hole as Norman struggled to reproduce his form of the opening three rounds. But the Irishman then hit the buffers himself and three straight bogeys allowed Norman to reclaim the lead as he headed to the tenth tee. KJ Choi, who had started the day tied for second place, slipped down the leaderboard after taking 40 shots, six over par, to reach the turn. But the South Korean was still not out of it - at ten over he was one of 11 players within four shots of the lead, a group that included 20-year-old English amateur Chris Wood. Norman's opening holes evoked memories of the 1996 US Masters, where he started the day six shots clear of the field and slumped to a 78 that left him five shots behind Nick Faldo. There were no signs of nerves as Norman split the fairway with his opening tee-shot. But he paid the price for depositing his second in a greenside bunker from the middle of the fairway while Harrington salvaged a four by leaving a chip inches from the pin. Wayward drives led to dropped shots at the 2nd and 3rd to hand Harrington the outright lead and the Irishman turned the screw with a textbook par on the 499-yard par four, the toughest hole on the course by some distance. Norman meanwhile was visiting the rough on both sides of the fairway before holing an eight footer to avoid a double bogey. The first chink in Harrington's steely armour came when the wind got hold of his tee shot at the short 7th and deposited the ball well to the left of the green, from where he was unable to get up and down. Norman also missed the green but holed an eight-footer for par to cut the lead back to one shot and suddenly it was Harrington who began to succumb to the pressure.At 53, Norman was bidding to become the oldest player to win a major.The Australian is five years older than Julius Boros was when he won the 1968 US PGA, seven years older than 'Old' Tom Morris when he secured the last of his four Open titles in 1867 and also seven years older than Jack Nicklaus when he was fitted for his green jacket at the 1986 US Masters. Harrington, who came from six shots back before beating Sergio Garcia in a play-off last year, is bidding to become the first European in over a century to successfully defend an Open title. If Choi can come through to win he will become the first Asian to win a major tournament. Conditions at Royal Birkdale were less testing than they had been on the first three days. But the breeze was still stiff enough for Open organisers to sanction a move to the forward tee at the par four 10th, adding to the three holes that were shortened on Saturday to give the players a better chance to finding the fairways.It was also still blustery enough to ensure that the nerves of the would-be history-makers would be tested to the maximum down the final stretch.Norman has attributed his extraordinary renaissance to the happiness he has found in his relationship and recent marriage to tennis legend Chris Evert. Throughout his opening three rounds he exuded a zen-like calm that certainly gave the impression of a man at peace with himself and the world. But he knows better than most that even the strongest swings and psyches can unravel in the final round of a major championship. His collapse at the 96 Masters was the most spectacular but it was not exactly unexpected - five times previously he had conceded a final day lead in major tournaments with his 1986 Open win the only time where he went on to win.