That tied the English former world number one with early starter DeLaet, who holed out a wedge shot from 109 yards to eagle the par-four ninth on his way to 67 on the Harbour Town layout.
European Ryder Cup stalwart Ian Poulter of England and 2012 U.S. Open winner Webb Simpson were two shots back at eight-under 134, one stroke better than five players including first-round leader Bud Cauley, who followed an opening 63 with 72.
Donald leaned heavily on his short game as he lost control off the tee, hitting just seven fairways yet grabbing a share of the lead in his quest to take the next step after four runner-up finishes here.
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"It was a little bit of a struggle today, but my short game
certainly bailed me out," Donald, 39, told Golf Channel.
"The greens are very small and you're not going to hit all of them, so you need to be good around the greens. I proved that the last couple of holes."
DeLaet, seeking his first PGA Tour victory after three second-place finishes and three thirds, vaulted up the leaderboard with a red-hot run around the turn.
"I had a nice little stretch in the middle of my round. I birdied eight, then there was the ninth. At 10, I missed an eight-footer for birdie, and I birdied 11 and 12," he said.
DeLaet is one of eight players to have accumulated $10 million in earnings without a victory.
Donald said winning on Sunday would bring vindication.
"Would be a little bit of coming back to what I really feel like I can play," he said. "The last couple of years have been a struggle, but I still feel like I've got some good years in me. I need to try and finish it off this weekend."
(Reporting by Larry Fine in New York; Editing by Peter Rutherford)
