EDISON - Jason Day romped to a six-stroke victory in the Barclays on Sunday, firing an eight-under par 62 to seize the lead in the US PGA Tour’s FedEx Cup playoff chase.

The Aussie, who ended a run of major heartbreak with his first Grand Slam title at the PGA Championship this month, backed up that triumph in style. He fired eight birdies without a bogey en route to a 72-hole total of 19-under 261 at Plainfield Country Club. Masterful on the greens, Day rolled in birdie putts of 28 feet or more at the 10th, 14th and 15th in a dominant performance in the first of four tournaments in the season-ending playoffs — in which a $10 million bonus will go to the series winner after the Tour Championship in September.

Sweden’s Henrik Stenson was a distant second after a 66 for 267. Stenson tried to keep things interesting, shaking off an early bogey with three straight birdies starting at the fifth, then trimming Day’s four-shot lead to two after birdies at the 10th, 13th and 14th. But Day plumped his cushion back to three strokes with a 28-foot birdie bomb at 14, and after Stenson bogeyed the par-five 16th to fall four back it was clear sailing for Day.

He didn’t take his foot off the gas, rolling in a 33-foot birdie putt at 15 and draining a 10-foot birdie at the last. “I’m just trying to improve each and every week,” Day said.

“To be able to play the way I did over the weekend here was fantastic. Today was just phenomenal golf.” Two-time Masters champion Bubba Watson was alone in third after a 69 for 269.

Watson overcame a double-bogey with three back-nine birdies, a birdie at the last moving him ahead of British Open champion Zach Johnson and Zac Blair, who shared fourth on 270. Johnson signed for a 69, while Blair moved up with a four-under 66. Bae Sang-Moon of South Korea, who shared the overnight lead with Day, made a promising start with a birdie at the second, but bogeyed five of his next eight to see his challenge end.

He carded a two-over 72 to share sixth place on 271 along with Americans Daniel Summerhays (66) and Ryan Palmer (70). Day, who narrowly missed out on reaching a playoff at the British Open, has won three titles since — the Canadian Open along with the PGA and the Barclays. He had won at Torrey Pines in February, and has now matched Jordan Spieth’s four US tour titles this season. Since 2010, the only other players to post four or more wins in a season are Tiger Woods and Rory McIlroy.

Day jumped over Spieth to the top of the playoff standings. The 22-year-old American, winner of the Masters and US Open this year, missed the cut and fell not only from the top of the playoff race but also from the world number one ranking, handing it back to Rory McIlroy after just two weeks. With the win, Day — who rose to a career-high number three in the world with is win at Whistling Straits — thrust himself into the world number one conversation, along with McIlroy and Spieth. “It’s been a special summer for me — and it’s not over,” Day said.