The WGC-Accenture World Match Play champion from England moved to seven under for the week at Augusta National with 18 holes remaining, five adrift of Ryder Cup teammate Rory McIlroy.
"When I got to three under through nine I thought I could maybe sneak a couple on the back nine, but I didn't play the par fives quite well enough today, even par, but still a very solid day," said the 33 year old.
"It's put me in a good position, I've still got a great chance tomorrow, which is always the goal at Majors to be in contention and have a chance.
"I know some guys were making some birdies, but they certainly weren't running away. And again, I would have loved to have snuck a couple more, but that's how it is."
Donald is hoping to use his experience from previous Majors to overcome the 21 year old Northern Irishman.
"When Zach Johnson won (in 2007) I was around the same I think," he added. "I know playing the ninth, I was one shot out of the lead and made a triple there and ended up finishing tenth that year.
"I'm always learning. Just to stay within yourself, try to stay patient, be aggressive when you can, don't be afraid to make mistakes."