Sixth, fourth and sixth in his last three events, but still without a victory in 198 European Tour events, Donaldson went to the turn in 32 to improve from one under par to five under.
The 34 year old, a team-mate of Luke Donald and Paul Casey when Great Britain and Ireland finished second in the world amateur championship ten years ago, birdied the second, fifth, eighth and ninth.
Down in joint 49th place at halfway, Donaldson was up into a tie for 15th, but still five adrift of Swede Johan Edfors.
Ten under following his dazzling second round 64, Edfors teed off again one in front of England's Mark Foster and Spaniard Sebi Garcia, who is ranked 1,272nd in the world and is playing this week on a sponsor's invitation.
From Majorca and with an English mother, Garcia had a round of 58 during a Spanish mini-tour event in December, although placing of the ball was allowed at the time.