(Reuters) - Dustin Johnson followed up his U.S. Open victory in style, taking advantage of a late stumble by Jason Day to secure a one-stroke victory at the WGC-Bridgestone Invitational in Akron, Ohio on Sunday.

Suddenly the hottest player in the game, long-hitting Johnson stormed home with a 66 on the demanding Firestone course to finish at six-under-par 274, while fellow American Scott Piercy (70) birdied the last to claim second place on five-under.

Piercy also finished runner-up to Johnson two weeks ago at the U.S. Open.

World number one Day struggled with his swing for much of the week, and it finally caught up with him at the par-five 16th, where he ran up a double-bogey after pulling his three-wood tee shot and then compounding his problems by hitting his third shot into the pond guarding the green.

Australian Day (72) finished three shots behind Johnson, equal third with Americans Jordan Spieth (67), Matt Kuchar (66) and Kevin Chappell (67).

“I played good this weekend,” the 32-year-old Johnson told CBS television after clinching his 11th PGA Tour win.

It was also his third win in a World Golf Championships events. Only Tiger Woods (18) has more WGC victories.

“I thought I drove it really well. I had a lot of shots from the fairway, which is what you have to do around here. I rolled the ball really well today."

Johnson, who is projected to overtake Spieth in second spot when the world rankings are updated on Monday, will be brimming with confidence when he heads to the British Open at Royal Troon in Scotland in less than two weeks, after a few days in Ireland en route.

“I feel great. I feel my game is where it’s been all year," he continued.

"I’ve played solid all year. I just haven’t been putting as well as I’ve liked to. The last couple of weeks I’ve just putted well and my game shows it.”

Day, who began the day sharing the lead with Piercy, could not add to his total of eight wins in the past year.

He continued to struggle off the tee at the tight Firestone layout, hitting only eight of 28 fairways in his final 36 holes.

“Sixteen is always a tough par-five anyways if you don't get a good drive there,” Day said. “It's really tough to get any sort of wedge in your hand and I kind of made a mess of it.

“I played pretty good golf up until 16. I really had two bad holes. I mean, I had a couple bogeys, but really kind of one hole that derailed me, which was 16.”

(Reporting by Tim Wharnsby in Toronto; Editing by Andrew Both)