The 23-year old world No 1 closed with a stunning, five-under-par 67 to win by two shots from Westwood and Phil Mickelson (70) on 20 under par, clinching his fourth PGA Tour win of the season and his third in a run of four events that began with his runaway eight-shot US PGA Championship triumph 28 days ago.
As Graeme McDowell and Pádraig Harrington failed to make the top-30 in the FedEx Cup race who qualified for next week’s Tour Championship in Atlanta, McIlroy became the first player to win back-to-back events on the US Tour since Tiger Woods in 2009
More remarkably, only Woods (who tied for fourth on 17 under after a 68) and Jack Nicklaus have won more events before by the age of 23.
While Woods won an incredible 15 times before his 24th birthday, McIlroy needs ‘just’ two more wins between now and May 4 next year to match the Golden Bear, who triumphed eight times on the US Tour before he turned 24.
McIlroy now matches Ryder Cup skipper Jose Maria Olazabal and Scot Sandy Lyle with six US Tour wins in just his 53rd start — one more victory than Harrington.
A shot behind leader Vijay Singh entering the final round, McIlroy stormed to the turn in three-under 33, then birdied the 10th with a glorious 129-yard approach to four-and-a-half feet to take the outright lead.
Playing partner Westwood drew level on 19 under with a birdie from 14 feet at the par-three 13th, leaving them two shots clear of Mickelson and overnight leader Singh and setting up an enthralling finish.
But Westwood failed to get up and down at the 14th, leaving McIlroy one clear with four to play.
Smelling blood in the water, McIlroy moved two clear when he comfortably two-putted from 13 feet for birdie at the par-five 15th as Westwood overshot the green.
He then moved three clear with another birdie at the 16th, holing from 14 feet as Westwood missed from just 12 feet.
Three clear of Westwood and Mickelson playing the last, McIlroy could afford to make his only bogey of the day and still capture the $1.4m top prize to take his earnings on the PGA Tour this term to $7.8m
“I never really thought about [winning six times before my 24th birthday],” said McIlroy. “I just went out to play as well as I could and I knew if I played to the best of my ability I would win events.
“I didn’t think it would happen so quickly but I am just on a great run at the minute and trying to keep that going as long as possible.”
It was a tournament to forget for McDowell and Harrington as they failed to secure the top-five finishes they needed to qualify for Atlanta.
Harrington finished tied 16th after a closing 73 while McDowell crashed to a nightmare six-over 78 for a share of 34th on six under.