Shane Lowry held off the challenge of three major champions to claim the biggest victory of his career in brilliant fashion in the WGC-Bridgestone Invitational.

Lowry carded a flawless final round of 66 at Firestone Country Club to finish 11 under par, two shots ahead of double Masters champion Bubba Watson, with Justin Rose and Jim Furyk another two shots back after disappointing rounds of 72.

"It's hard to believe but I played good today," Lowry told Sky Sports 4. "I was quite nervous out there towards the end but made a lot of good decisions, hit the ball well and got a bit of luck as well which was nice.

"It's great to be able to pull something off. I was kind of doubting myself a little this year, things haven't been going my way but when you come out the other end it's always nice.

"I played as good a golf as I've ever played the last four days," he added.

Lowry began the final round two shots off the lead shared by former US Open champions Rose and Furyk, but wiped out the deficit with birdies on the second and eighth.

And when he produced a spectacular recovery following a wayward tee shot on the 10th, the resulting tap-in birdie gave the 28-year-old a two-shot lead over the chasing pack.

Watson then recorded his fourth birdie in six holes on the 13th to close within a shot and Furyk did likewise with a birdie on the 11th, only to promptly bogey the next after chipping from one side of the green off the other.

And when Watson also dropped a shot on the 15th, Lowry was two in front again and maintained that advantage with a superb par save from 20 feet on the 14th after finding a fairway bunker off the tee.

"That was massive," Lowry admitted. "The bunker was pretty dead and even with my pitch I could not go at the flag and just had to hope to hole a long putt."

Watson closed within a shot once more thanks to a brilliant birdie on the 17th, following a wild drive with a superb approach up and over a tree to within seven feet of the hole.

A drive of 379 yards down the 18th gave Watson the chance of another birdie, but this time his approach finished 25 feet from the hole and the left-hander had to settle for par.

The resulting 66 set the clubhouse target at nine under par and left Lowry needing to par the final two holes for victory. He held his nerve to hole from five feet on the 17th but looked to be in trouble when he pulled his tee shot on the last into the trees.

However, the former Irish Open champion - he was still an amateur when he won the title in 2009 - found a good lie in the rough and powered a wedge over the trees to 11 feet, from where he holed for a birdie to make certain of the first prize of $1,570,000.

"I was trying to get it on the front right of the green but pulled it a little bit, it went through the tree and rest is history," Lowry added.

Rose was plagued by a poor performance on the greens, three-putting the long second for par and, after getting back into contention by chipping in on the ninth, also three-putting the 10th from just 15 feet.

Furyk recorded his 10th top-10 finish in the Bridgestone but has now failed to win 10 tournaments in succession in which he led or shared the lead after 54 holes.

Jordan Spieth had set the early clubhouse target on four under after a final round of 66, but that was never going to be enough for the victory which would have seen him replace Rory McIlroy as world number one.

However, the 22-year-old Masters and US Open champion was relishing playing alongside McIlroy in the first two rounds of the US PGA Championship at Whistling Straits, with McIlroy returning from injury in time to defend his title.

"It's going to be great," Spieth told Sky Sports 4. "I'm very very happy that he is back, everybody is. He certainly takes the interest in the game to a different level.

"It will be cool to battle it out with him, hopefully for the number one spot if it comes down to Sunday. I am certainly ready to be in that position and hopefully we can do so."