He was No 1 in all but name before the start but as Tiger Woods limped away with a recurrence of his back injury to vacate the throne, Rory hit Sergio Garcia with four thunderous blows in the first five holes and officially claimed the crown as he became only the second player since Woods to win a major and a WGC back-to-back when he claimed the Bridgestone Invitational by two strokes at Firestone on 15 under par.
The Open champion's closing 66 was as impressive as it was expected — massively long, arrow-straight driving and towering irons on a soft golf course — as he overturned a three stroke deficit with respect to Garcia (71) thanks to a vicious opening flurry of blows you'd expect from Marvin Hagler in his prime.
Four birdies in his five holes put him two clear and while Garcia drew level with nine to go when McIlroy bogeyed the eighth and he birdied the ninth, he fell one behind again when McIlroy birdied the 11th and then lost the title with a pulled tee shot leading to a fatal bogey at the par-three 16th.
European Ryder Cup skipper Paul McGinley watched this driving exhibition in awe from a Sky Sports studio and described McIlroy's driving all week as the best performance he had ever seen.
The 25-year old lives and dies by that club and in averaging 334 yards off the tee, making him longer than anyone in golf including Bubba Watson, he destroyed Garcia by hitting nine of 14 fairways and then peppering the pins.
Five shots behind Garcia with three holes to play on Saturday night, McIlroy found himself one clear of the Spaniard after just three holes of the final round and two ahead after five before easing off the gas.
"Yeah that was a huge stretch of the golf tournament," McIlroy said of his birdie-biride-birdie-par-birdie start. "To birdie the last two last night and then they way I started today — four under through the first five — I just started really, really well and put some pressure on Sergio early."
McIlroy was not quite at his very best on the back nine, getting lucky twice as the trees spat two wayward tee shots into the fairway.
But he was clinical when he had to be, holing four clutch putts in a five hole stretch — from eight feet for birdie at the 11th to regain the lead, and from five, four and six feet respectively for par at the 13th, 14th and 15th to stay in front before Garcia folded at the 16th.
"I rode my luck a little bit on the back nine," McIlroy said after regaining the world No 1 spot from Adam Scott and going back to the top for the first time since March 2013, the week after he walked off the course at the Honda Classic saying he wasn't "in a good place mentally."
"Sergio had some putts to get close to me and I had a couple of tree limbs that went my way. But I played another really solid round of golf and I'm just really pleased to get my first World Golf Championship so soon after winning the Open."
Asked about the importance of his driving, McIlroy said: "I've said it all week. That's the foundation of my game. When I drive it like that I've a pretty good chance to win most week and I've showed that the last couple of weeks and hopefully I'll go to Valhalla in good form and trying to get three in a row."
There was steely look of determination about McIlroy right from the start.
At the first he pulled his tee shot into the trees but with just 74 yards to go, he conjured up a low chipped approach that ran up to three feet and he duly hold the putt to get within two of Garcia.
At the second he blasted the ball 20 yards past Garcia and two putted from 27 feet for birdie to get within one before taking the outright lead at the third where the Spaniard bogeyed and McIlroy followed a 330 yard bomb with a 120-yard approach to nine feet and holed the putt.
He could have birdied the fourth but missed an 11 footer. But he was soon two clear when he 212-yard approach to six feet at the fifth and rolled him the putt to get to 15 under.
He handed Garcia a shot back at the eighth, where he bunkered his approach from the right rough and missed from 11 feet.
When Garcia birdied the ninth from 12 feet and McIlroy lipped out from six to leave them tied heading into the back nine, there was a still a glimmer of hope for Garcia.
But McIlroy wore him down under a barrage of huge drives and unerringly accurate approach shots, breaking his will.
After outdriving him by 40 yards at the 11th, McIlroy birdied from 11 feet to regain the lead and made sure he remained in front with some crucial par saves as Garcia missed birdie chances from 10 feet at the 10th and eight feet at the 11th.
The man from Castellón had to hole an 11 footer for par at the 12th to remain in touch but didn't hit one close again until he was two behind at the 17th.
He missed form 11 feet and McIlroy two putted the last for par and victory.
"What I'm really proud of is following up The Open with a performance like this," McIlroy said. "I didn't want to feel any let down. I wanted to just keep going and keep performing well until the end of the season.
"It's great to come to one of my favourite tournaments of the year because I love the golf course here in Akron and to perform like this, I'm very satisfied."
it was also a memorable week for Graeme McDowell as he closed with back to back 66s for a career best share of eighth place on seven under par to boost his chances of qualifying for the Ryder Cup.
“The game has slowly improved over the last couple of months,” said McDowell, whose previous best finish of 22nd came in 2010. “I'm at that point now where I'm starting to believe that I can hit the shots to win any given week if I put it all together. I'm in a good place mentally and physically and looking forward to the PGA Championship next week and beyond.
“I stuck to my guns and played light in the spring, but pulling out of Wentworth was a tough decision in my schedule this year. It's paying off now though, and The European Tour were great with me.
“They understood where I was coming from as I wanted to spend some time with my family before I played this heavy part of the schedule, with my wife at home not being able to travel. I’ve paced myself well, and thankfully it's paying off now.”
On his Ryder Cup standing, he said: “It's something that ticks along in the background for me. It's something I'm very much looking forward to, and to play my fourth Ryder Cup would be a huge honour. I have come into good form this summer, so hopefully Captain McGinley is watching and feels I can be an instrumental part of the Ryder Cup team.
“I'm getting to the veteran stage now, and I feel like I can definitely be a decent sort of leader for the young guys on the team. I'd like to play my way on out of my own merit as opposed to waiting for a pick, so that's what I'm focused on the next few weeks.”
With this win - Rory McIlroy
SUNDAY AUGUST 3, 2014 – WGC – BRIDGESTONE INVITATIONAL
* His eighth European Tour International Schedule victory in his 139th European Tour event.
* Moves to Number One in the Official World Golf Ranking from second.
* His third European Tour victory of the 2014 season, following the BMW PGA Championship and The 143rd Open Championship.
* The first time he has recorded three European Tour victories in the same season.
* The first player to win three events on The European Tour International Schedule in the 2014 season.
* His first World Golf Championship title in his 22nd WGC appearance.
* This victory beats his previous best WGC performance of second in the 2012 WGC – Accenture Match Play Championship. (His previous best WGC stroke play finish was third in the 2012 WGC – Cadillac Championship.
* Victory comes in his sixth WGC – Bridgestone Invitational appearance.
* This victory beats his previous best WGC – Bridgestone Invitational of tied fifth in 2012.
* Continues with his wonderful record at Firestone’s South Course. Was tied ninth in 2010, tied sixth in 2011, tied fifth in 2012 and first in 2014.
* From his 22 WGC appearances he has finished in the top ten on 13 occasions.
* Becomes the second Northern Irishman to win the WGC – Bridgestone Invitational, following Darren Clarke in 2003.
* Becomes just the second European Tour to win the WGC – Bridgestone Invitational, following Darren Clarke in 2003.
* Becomes the fifth player from the United Kingdom to win a WGC event, following Darren Clarke (2000 WGC – Accenture Match Play Championship and 2003 WGC – Bridgestone Invitational), Luke Donald (2011 WGC – Accenture Match Play Championship), Ian Poulter (2010 WGC – Accenture Match Play Championship and 2012 WGC – HSBC Champions) and Justin Rose (2012 WGC – Cadillac Championship).
* Becomes the ninth different player to win the WGC – Bridgestone Invitational.
* Becomes the 11th different European Tour Member to win a WGC event.
* Becomes the 14th WGC victory by a European Tour Member.
* Becomes the 29th different player to win a WGC event in the 52nd playing of an individual WGC event.
* Joins Tiger Woods (1999), Craig Parry (2002), Stewart Cink (2004), Vijay Singh (2008), Hunter Mahan (2010), Adam Scott (2011) and Keegan Bradley (2012), as players making the WGC – Bridgestone Invitational their first WGC title.
* Becomes the 14th different player to win a Major Championship and a WGC title.
* Joins Darren Clarke, Ernie Els, Martin Kaymer, Justin Rose and Vijay Singh as European Tour Members to win both a Major Championship and a WGC title.
* Aged 25 years and 91 days becomes the youngest European winner of a WGC event.
* Began the final day three shots behind Sergio Garcia. Becomes the 20th player this season to win after making up a final round deficit.
* Now has won in his last two European Tour appearances, following The Open Championship. Is the first time he has won in consecutive European Tour appearances.
* The first player to win The Open Championship and win again in their next European Tour appearance since Tiger Woods. The American won The Open in 2006 and won on his next European Tour outing at the US PGA Championship.
* Becomes the first player to win in consecutive European Tour appearances since Phil Mickelson at the 2013 Aberdeen Asset Management Scottish Open and The Open Championship.
* Only be the third of his eight European Tour wins where he has made up a final round deficit to win. Made up seven to win the 2014 BMW PGA Championship, three to win the 2011 Hong Kong Open and three at the 2014 WGC – Bridgestone Invitational.
* The 53rd Northern Irish win in European Tour history.
* The fourth Northern Irish victory of the season. They are: Rory McIlroy (BMW PGA Championship, The 143rd Open Championship and WGC – Bridgestone Invitational) and Graeme McDowell (Alstom Open de France).
* Becomes the tenth player in European Tour history to win more than €20 million in European Tour Official Career Earnings
* Moves to 434.26 in The Ryder Cup World Points List.
* The 14th victory as a professional.