The Englishman, currently ranked number three, can take over at the head of the global rankings with victory this week, even if World Number Two Lee Westwood wins in Indonesia due to more ranking points being available in south Carolina.
Donald, who has finished in the top five at four of his last five events, started at the tenth and was level par after his first nine holes as he followed a birdie at the par three 17th with a bogey at the 18th, but his front nine proved to be better as he racked up four birdies to lie just three shots behind leader Garrett Willis.
Willis, who had pondered switching to a belly putter before electing to stick with his conventional club, enjoyed a brilliant run of six-straight birdies between the second and seventh and went on to pick up three more shots on the back nine, only suffering blemishes at the ninth and 11th to hold a one shot lead at seven under par.
He is being chased by a four-strong group at six under made up of America's Chad Campbell, Tim Herron and Mark Bettencourt, along with India's Arjun Atwal.
Donald's compatriot Brian Davis, who missed out on this title last year after calling a foul on himself during a play-off, was at three under along with Northern Ireland's Graeme McDowell.
Ian Poulter was at two under after a mixed round that included five birdies and three bogeys, one shot ahead of Masters Tournament contender Jason Day.
Colombia's Camilo Villegas was among the group tied for third at five under, partly due to an oustanding eagle at the par five fifth which saw him chip in from 43 feet.