It was McIlroy's first tournament victory since the Irish Open in May and his first title on American soil since winning the Wells Fargo in May last year.

The Northern Irishman emerged from the packed leaderboard as strong winds turned the final round at TPC Boston into a battle of survival. That is all except McIlroy and Adam Scott, who both fired the lowest round of day. For Scott, his 65 catapulted him 19 spots up the leaderboard into outright fourth. For McIlroy, his stellar round saw him easily make up the six shots he trailed leader Paul Casey by after 54 holes.

With strong winds and rain forecast, PGA Tour officials moved the final round tee times forward to avoid any delays. While the rain didn’t come, the wind played its part and proved advantageous for McIlroy, who is accustomed to playing in similar conditions around his favourite Royal County Down course. But even he admitted later: “If it was like this at home, I’d be reluctant to play.”

Rory McIlroy high-fives some young fans during the final round. PHOTO: David Cannon/Getty Images

While McIlroy was brilliant, his surge to breaking his victory drought was made easier by the fall of the leading contenders. McIlroy, PGA Champion Jimmy Walker and James Hahn were the only players in the last four groups to shoot under par for the final round.

Olympic gold medallist Justin Rose was in the thick of the action as he got to 11 under through 10 holes but then played the final eight holes in 10 over, including triple bogies at the 13th and 16th holes along with a double bogey at the par-4 12th. His back nine score of 45 was 11 shots worse than his front nine score.

FINAL LEADERBOARD | FEDEX CUP STANDINGS

The final group —Casey (73), Smylie Kaufman (76) and Brian Harman (77) — were a combined 13 over for the round.

McIlroy, who was four over through his first three holes of his opening round, played the next 69 holes in 19 under, which he can put down to a much-improved performance with the putter. He ranked 70th in putting at the Barclays last week, but finished seventh for the same stat at TPC Boston. The dramatic improvement comes just a week after the now World No.3 changed to a Scotty Cameron putter and employed a new putting coach.

The 27-year-old opened his final round account with a birdie at the 2nd hole before adding more birdies at the 4th, 7th, 8th and 9th holes to make the turn in 31. Another birdie at the 12th gave him the outright lead for the first time and, although he dropped a shot at the 17th, he made a brilliant up-and-down from the greenside bunker for birdie at the par-5 18th.

"From three holes in – four over par – there were a lot of things going through my mind, and one of them was not winning this tournament,” McIlroy said. "So 69 holes later – I played some great golf and holed some great putts. I'm just really proud of myself, how I hung in there on the first day and then got some momentum on Saturday. Then I just went with it."

"It's nice to get that first win in the States this year and hopefully I can take this momentum into the next couple of weeks and ultimately the Ryder Cup." - Rory McIlroy

Casey struggled to fend off the surging McIlroy and his closing 73 saw him finish two shots adrift of McIlroy in outright second. Walker was a further shot back in third place at 12 under.

Casey, who was seeking his first PGA Tour win since 2009, began poorly with bogies at the 2nd and 5th holes. He holed a nice 12-foot putt for birdie at the 7th but missed a four-footer for par at the 11th hole to hand that shot back.

The Englishman, playing two groups behind McIlroy, was still within two strokes of the lead playing the final hole and found the green on the par-5 with his second shot. However, his eagle putt from 58 feet raced by the hole and he missed the return putt before tapping in for par.

McIlroy plays a brilliant bunker shot at the last hole to set up a tap-in birdie putt. PHOTO: David Cannon/Getty Images

“It was absolutely an amazing round of golf in those conditions,” said Casey in tribute to McIlroy’s performance. “It shows you just how good Rory is. Really stellar stuff.

“I found it incredibly difficult out there … I never felt like I had any rhythm.”

McIlroy has stormed from 38th to fourth place in the FedEx Cup standings, while Patrick Reed still leads over Jason Day and Dustin Johnson. Scott picked up valuable points and is fifth in the standings with two events left in the play-offs.

The play-offs now move to Crooked Stick GC in Indiana for the BMW Championship. Interestingly, when McIlroy last won the Deutsche Bank at TPC Boston in 2012, he went onto the win the BMW the following week at Crooked Stick, which was the last time that course hosted the event.