ORLANDO (REUTERS) - Jason Day crowned a brilliant back nine with an eagle at the 16th to seize a one-stroke lead with a six-under 66 in Thursday's opening round of the Arnold Palmer Invitational in Orlando, Florida.

The Australian world No. 3 powered a six-iron from 197 yards away to 10 feet and rolled in the putt for an eagle-three on the par-five, posting a five-under 31 on the back nine on a warm, sunny day at Bay Hill.

The blazing finish by the reigning PGA Championship winner vaulted him ahead of an impressive group at five-under that included compatriots Adam Scott and Marc Leishman, Sweden's Henrik Stenson and Americans Brendan Steele and Troy Merritt.

"I drove it on a string, and played the par-fives in five-under," said the long-hitting Day. "It was one of those days where everything kind of went well."

The red-hot Scott, winner of his last two events, again showed command of the short stick since having to give up his anchored putter this year, saving par twice from five feet, once from 10 and once from 12.

"The course is perfect so I had to take advantage of the morning conditions," Scott told the Golf Channel. "I didn't play my best golf tee to greens, but I chipped and putted really well."

World No. 6 Scott has been in a zone, following a second-place finish at Riviera with victories the next two weeks at PGA National and Trump National Doral before taking a one-week break.

Ten players were bunched two strokes off the pace after shooting four-under rounds of 68, including former US Open champion Justin Rose, fellow Briton Paul Casey, Italy's Francesco Molinari and K.J. Choi of South Korea.

Rose had a pair of eagles, including one at the par-four third, his 12th hole of the day, from 112 yards to compensate for a double-bogey on his second hole.

Two-time defending champion Matt Every shot a one-under 71 while world No. 2 Rory McIlroy was tied for 107th in the 120-man field after a three-over 75.