Donald won the tournament after emerging victorious from a four-way play-off against Jim Furyk, Robert Garrigus and Sang-Moon Bae after the quartet had all finished on 13 under par.
McIlroy tweeted his congratulations within minutes of Donald's victory, posting: 'Well I enjoyed it while it lasted! Congrats @LukeDonald! Impressive performance!'
No 1: Luke Donald celebrates his winning putt
How golf's world No 1 spot has changed in the last 17 months
October 24 2010 - 1 Woods 8.31, 2 Westwood 8.25, 3 Kaymer 8.03
October 31 2010 - 1 Westwood 8.29, 2 Woods 8.13, 3 Kaymer 7.98
February 27 2011 - 1 Kaymer 8.35, 2 Westwood 8.16, 3 Donald 6.63
April 24 2011 - 1 Westwood 7.65, 2 Kaymer 7.52, 3 Donald 7.38
May 29 2011 - 1 Donald 9.14, 2 Westwood 8.74, 3 Kaymer 7.40
March 4 2012 - 1 McIlroy 9.30, 2 Donald 8.97, 3 Westwood 8.19
March 18 2012 - 1 Donald 10.03, 2 McIlroy 9.85, 3 Westwood 8.16
A run of five birdies in the first 11 holes on Sunday moved Donald into contention, before he consolidated with seven successive pars to make sure of a 16th top-10 finish in his last 22 events.
He hit an excellent approach shot on the first hole of the play-off with a seven iron from the rough - and holed the putt to make sure of the victory.
Robert Garrigus had also given himself a birdie opening - but the American's chance had gone when the putt went past the hole.
Donald's victory made it three European victories in a row in America after McIlroy triumphed at the Honda Classic and Justin Rose did likewise at the Cadillac Championship.
Give us a kiss: Donald puckers up with the trophy
Donald admitted the win was a morale booster ahead of the Masters.
He said: 'I feel like I've achieved a lot in my career but this is perfect preparation. I've got two weeks off now and can look forward to Augusta.
'I certainly was a lot more nervous about getting to number one the first time. This time it wasn't my focus - I was focused on winning the tournament and it all worked out.'
Garrigus had given himself a chance of victory with birdies on the last two holes giving him a 13-under round of 64.
Bae, seeking to become only the third South Korean to win a PGA tour event, held the lead yesterday but a final-round 68 was enough to earn him a place in the play-off, while joint overnight leader Furyk managed a 69.
Fellow overnight leader Retief Goosen slipped out of contention, finishing on seven under after a final round 75.
Promising signs: Donald heads to Augusta on fine form
Goosen, twice a winner of the event, made a poor start to his final round, with a double bogey on the first. He dropped another shot at the next hole and failed to recover.
Ernie Els appeared to be in a good position when he held a narrow advantage with two holes to play but a pair of bogeys on the final two holes ended his hopes of victory and saw him finish a shot off the pace alongside Scott Piercy, Jeff Overton and Ken Duke.
Piercy hit the round of the day, a nine-under-par 62 to claim a share of the lead. The 33-year-old birdied seven birdies in his first nine holes today and added two more at the 14th and 16th.