Willett was three clear after eight holes of the final round, but fell one behind after bogeys at the ninth, 11th and 15th.
Fraser dropped a shot at the difficult 456-yard last, however, and Willett got away with a bad drive close to the trees for a par to tie on the 11 under par mark of 277. They were round in 71 and 73 respectively.
They then played the 18th on four more occasions. Both parred it the first time after Fraser holed from 12 feet, bogeyed it next with Willett missing from four feet and parred it next before it was settled.
Willett was over the green and almost chipped in, then Fraser lipped out from 30 feet and missed his four-footer coming back.
Joint-third one behind were Ireland’s Paul McGinley (66), Spaniard Gonzalo Fernandez-Castano and England’s Chris Wood, who was joint leader with two to play, but bogeyed the short 17th en route to a 73.