World No. 1 Luke Donald stumbled in his bid at golf history on Friday as Justin Leonard, Henrik Stenson and South Korean Bi-o Kim shared the lead at the US PGA\'s season-ending event. US veteran Leonard, the 1997 British Open winner, fired a bogey-free nine-under par 63 to stand on 12-under 132 after 36 holes at the $4.7 million Children\'s Miracle Network Hospitals Classic at Disney World resort. Tour rookie Kim, trying to secure a place on the 2012 tour, fired a 65 while Stenson shot 64 to share the top spot. Britain\'s Donald, trying to become the first golfer to win the European and US PGA money titles in the same year, fired a 71 to fall from a share of the 18-hole lead into a share of 14th place at seven-under 137 through 36 holes. Donald leads second-place Rory McIlroy in the European Order of Merit by 1.6 million euros and he was atop the US list until American Webb Simpson moved ahead of him last week to stand on $6,200,243 and lead Donald by $363,029. The Englishman can finish no worse than a two-way share of second to win enough money to overtake Simpson, who shot 69 on Friday to match Donald on 137. If Donald wins the top prize of $846,000, Simpson would have to finish alone in second for $507,600 in runner-up money to deny Donald the title. If Donald finishes as the lone runner-up, Simpson must finish no worse than alone in eighth place, worth $145,700, to edge Donald. If Donald shares second for $413,600, Simpson needs at least a four-way share of 21st to stay on top.