The World Number Two - who will replace Lee Westwood at the top if he finishes above him this week - drove into a bunker on the 473 yard first, and could only hit his second into more sand.
That led to a bogey five for last year's runner-up at Wentworth Club, and brought him back to six under for the week.
Crucially, however, none of the chasing pack had made any significant gains. On five under Johan Edfors was waiting to tee off and Matteo Manassero was level par after three holes, with a two shot gap back to England's Ross McGowan and Spain's Alvaro Quiros.
Scotland's Scott Jamieson held the clubhouse lead on two under par after a signing for a second round 69.
The in-form 27 year Challenge Tour graduate, who recently topped the Category 11 re-rank, recovered from a double bogey at the 12th with three birdies in his last five holes and was level with Spaniard José Manuel Lara, Chile's Felipe Aguilar Northern Irishman Darren Clarke, France's Thomas Levet and England's David Howell.
The 18 year old Manassero, who incredibly could move into the top 15 on the Official World Golf Ranking with victory this weekend, birdied the par five fourth as Donald had done two groups ahead to stay within one.
Lara birdied the last two for a 70 which left him four under in the clubhouse, level with Quiros who birdied the third and fourth.
Westwood birdied the second and fourth and at one under was up into a share of 12th. But he bogeyed the next.
Donald's third bogey came on the short tenth and it cost him the lead when Manassero birdied the 11th to go one in front at six under.
Open de España champion Thomas Aiken came into the picture at four under, turning in a superb 31 after two birdies and an eagle on the fourth.
He shared third place with England's David Horsey and Spaniards Quiros and Lara.