Rory McIlroy moved to the top of the world rankings after winning the Honda Classic by two strokes in Florida.
The 22-year-old from Northern Ireland showed great resolve, dropping only one shot in a final round of 69 for a 12-under-par total.
He withstood a superb final day charge from Tiger Woods, the youngest man to reach the number one spot, who had two eagles in a 62 to share second.
Lee Westwood had five birdies and an eagle in a 63 for fourth place.
It was a final round full of character from McIlroy, who has grown significantly in stature since imploding at last year's Masters with a closing 80 having led by four shots going into the final round.
The Northern Irishman becomes the second youngest player to reach number one.
He claimed his first title as a 19-year-old at the Dubai Desert Classic in 2009, secured his first major at last year's US Open and also won the Hong Kong Open in December.
This season he reached the final of the World Match Play event in Arizona, losing to Hunter Mahan in the final last weekend.
The final round was brought forward because of the threat of thunderstorms but though the conditions were breezy in the early part of the day they eased and were played out in warm afternoon sunshine.
When veteran Tom Gillis bogeyed his second hole in succession at the 10th McIlroy had a comfortable four-shot advantage with eight holes to play.
However, McIlroy hit a wayward drive at the 12th and dropped his first shot in 23 holes when he missed from 15 feet for par.
The drama intensified when Woods, who collected an eagle and three birdies in his first 11 holes to move into contention having been nine shots off the pace in joint 18th overnight, birdied the 17th and 18th in vintage fashion.
Having holed a huge putt at the par-three 17th, the last of the famous Bear Trap holes, the 36-year-old landed an imperious iron shot from a hanging lie in the semi rough on the final fairway onto the front of the green and set up an eagle chance to take him within one shot of McIlroy.
He duly rolled the eight-foot putt into the centre of the hole and saluted the exuberant crowd with a trademark fist pump, but McIlroy restored a two-stroke cushion after pitching superbly from 92 yards to five feet at the 13th.
McIlroy found a perilous spot in thick rough to the right of the 14th green but produced a deft chip and run down the hill to three feet and comfortably saved par.
His tee shot at the next went left into the bunker but despite a stone near his ball he splashed out to six feet and calmly stroked in the putt.
At the 17th, another par-three with water guarding the green, McIlroy found the bunker with his tee shot but escaped magnificently again to three feet and holed the putt.
Another assured putt from four feet secured a closing par five and saw him replace Luke Donald as the new world number one.
Westwood, who played the first three rounds with Woods, also produced a superb final day display, a birdie chance slipping narrowly by at the 16th and another at the last for a round of 62 also passing agonisingly past the cup.
Joint halfway leader Justin Rose had reached nine under but found the water at the 15th, the first of the Bear Trap holes, and dropped another shot at the 17th to finish with a 70 and a share of fifth.
YOUNGEST TO REACH NO:1
21 Tiger Woods (US), 1997
22 Rory McIlroy (NI), 2012
26 Martin Kaymer (Ger), 2011
27 David Duval (US), 1999
27 Ernie Els (SA), 1997
28 Bernhard Langer (Ger), 1986
29 Seve Ballesteros (Sp), 1986