Donald saved par on Nos. 1 and 4 with clutch putting, and some accurate up-and-down play helped him make four birdies in a stretch of six holes.
''It was a nice, solid start,'' said the Englishman, who made six of his seven birdies in the first 10 holes. ''It was very tidy. Just a lot of solid golf. I gave myself a lot of opportunities.''
Donald fended off a challenge from McIlroy at the tournament last year to become the first player to clinch both the European and PGA Tour money titles. The Northern Irishman has repeated the feat this season, and he surged into contention Thursday at the $8 million event with three birdies on the back nine. The PGA Championship winner could have matched Donald, but his tee shot on the 18th went into a creek.
Gonzalo Fernandez-Castano of Spain and Marc Warren of Scotland are also at 6 under.
On a day when more than three-quarters of the field shot under par, there were plenty of other big names in the mix.
Lee Westwood, three-time major champion Padraig Harrington, 2010 PGA Championship winner Martin Kaymer and two others were at 5 under. Six players, including 2011 Masters champion Charl Schwartzel, were another shot behind.
McIlroy struggled on the front nine, making only one birdie, but turned it around coming home with a stretch of five birdies in seven holes. He is trying to emulate Westwood's feat in 2009 in which he won the money title and this tournament.
''I got off to a bit of a slow start but felt I was hitting the ball well enough to give myself opportunities for birdies. I just had to stay patient. I got it together on the back nine,'' McIlroy said. ''It's a great way to start. Obviously, I'm confident heading into tomorrow.''
With the money title decided, players are now counting on strong performances to help them move up the rankings. A top-30 finish gets them into the British Open, while the top 15 is enough for the U.S. Open. The top 10 on the European money list will receive a portion of the $3.75 million bonus pool.