Rory McIlroy took a stranglehold on the $10m FedEx Cup and made another mark in the history books when he outplayed old ‘enemy’ Lee Westwood in a thrilling back nine duel to capture the BMW Championship at Crooked Stick for his second PGA Tour win in a row and his third in four starts.

The 23-year old world No 1 closed with a stunning, five under par 67 to win by two shots from Westwood (69) 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 Padraig 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, missing just one fairway in a display of driving that would do justice to any BMW advertisement. Talk about the Ultimate Driving Machine.

As if to confirm McIlroy’s status as the game’s undisputed No 1, Woods finished three shots behind on 17 under after a closing 68 while overnight leader Vijay Singh finished five shots behind in eighth after a 73 and gallingly missed out on the Tour Championship by finishing 33rd in the FedEx Cup list.

It was all about McIlroy, who was thrilled with his sixth win in America and another imperiously dominant performance against the best players in the game.

Declaring his surprise that he has risen so far, so fast he said: “I never really thought about (winning six times before my 24th birthday). 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.

Lee Westwood looks blankly into the distance after Rory McIlroy went three shots clear with two to play thanks to this birdie at the 16th.“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.

“The play-offs are big. You have the best players in the world up there. Last week it was myself, Louis (Oosthuizen) Tiger and DJ. This week it was myself, Phil, Lee, DJ, Tiger, Vijay. The fields are really deep and it is great to be able to win events where the quality of the field is so good.”

Set to play with Woods in the last group in the Tour Championship next week, McIlroy confessed that it was crucial to be successful in America, where he is now a firm fan favourite.

“I feel likeI have got tremendous support on the PGA Tour everywhere I go,” said McIlroy, who can still lose the FedEx Cup title despite his two wins. “I feel like this is where I belong. I’ve always wanted to play on the PGA Tour and it’s working out pretty good so far.”

Only Woods and Jack Nicklaus have won more events before by the age of 23 in the last 52 years.

While Woods won an incredible 15 times before his 24th birthday, McIlroy needs “just” two more wins between now and 4 May 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. He has one more victory than Harrington, for example.

A shot behind leaders Mickelson and Singh entering the final round, the Holywood star 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 Singh and setting up an enthralling finish.

The key to McIlroy’s victory came over the next three holes. At the 14th, he followed Westwood in missing the green but chipped to five feet and saved par as Westwood came up nine feet short and bogeyed. Once again, the Englishman’s unwieldy short game had let him down.

One clear with four to play and sensing 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 and failed to get up and down again

McIlroy then moved three clear with another birdie at the 16th, holing from 14 feet as Westwood missed from just 12 feet.

Mickelson made two birdies to close within two but bogeyed the 17th, where McIlroy had holed a clutch six footer for par to go to the last with a three shot lead.  The Ulsterman 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

But while it was another great week for McIlroy, it was a tournament to forget for McDowell and Harrington as they failed to secure the top-five finishes the need to make the top 30 in the FedEx Cup who qualified for next week’s Tour Championship in Atlanta.

Harrington finished tied 16th on 10 under par after a closing 73 that left him 43rd in the FedEx Cup standings while McDowell was 42nd after crashing to a nightmare, six over 78 for a share of 34th on six under.

The 41-year old Dubliner birdied the first from 25 feet but bogeyed the second off a bunkered tee shot and dropped another shot at the seventh when he failed to get up and down from left of the green.

Bunkered off the tee again at the par-five ninth, he splashed out and made birdie thanks a spectacular 167-yard approach to two and a half feet.

But he simply didn’t hit it close enough with his short irons on the back nine and while he birdied the par-five 15th, he double bogeyed the short 17th when he failed to reach the green with his chip and missed a four footer for bogey - a familiar story this season.

It was an even tougher day for McDowell, who was tied for ninth overnight and provisionally 33rd in the projected FedEx Cup standings.

But the Portrush star bogeyed the first and fourth before getting up-and-down from 96 yards for birdie at the fifth.

Desperate for birdies, he was poor off the tee when it matter and bogeyed the eighth, 10th and 11th to kiss the Tour Championship goodbye.

A birdied at the 12th hardly mattered and like Harrington he double bogeyed the par-three 17th, taking three to reach the putting surface from the cloying greenside rough, before dropping another shot at the last.