Americans Ryan Moore and Ben Crane also finished off 67s as 63 players returned to Liberty National early Friday after having their opening round suspended by failing light following more than six hours of delays due to thunderstorms.
They took best advantage of rain-softened conditions at the course set on the edge of New York harbour among those finishing the first round but stood three shots off the pace set by unheralded American Kevin Stadler.
Tied for second in the clubhouse at 65 were Henrik Stenson of Sweden, Colombian Camilo Villegas and American Ryan Palmer.
Another shot back were American Matt Kuchar and Australian Jason Day, with world number one Tiger Woods among 10 players three shots off the pace.
Friday's early starters were going right back out for the second round, while Woods and other players from the morning wave on Thursday were teeing off late in the afternoon to begin their next round.
Donald soared up the leaderboard with four birdies in five holes from the 12th, while Simpson and Moore birdied their last holes.
Crane, who barely scraped into the elite field for the FedExCup playoffs qualifying in 125th and last place, reached five under par before dropping a shot with a bogey at the 16th.
The 37-year-old Crane, a four-time winner on the PGA Tour sed an eagle at the par-five sixth to aid his charge.
Former PGA champion Martin Kaymer of Germany returned to complete a three-under 68, one shot better than Australians Adam Scott, Aaron Baddeley and Stuart Appleby.
Masters champion Scott and Baddeley both had eagles on their scorecard, with Baddeley holing out from 120 yards at the par-four first hole and Scott knocking his approach at the par-five 13th inside five feet.
British Open champion Phil Mickelson reached three under par after a birdie at the 10th, but three bogeys on the way in left him even par for the round.
(Reporting by Larry Fine, Editing by Steve Keating)
