Rory McIlroy struggles as Jason Day leads at Bay Hill

Jason Day is the current world number three

Rory McIlroy is nine shots behind leader Jason Day after round one of the Arnold Palmer Invitational at Bay Hill.

The world number two started with a double bogey after hitting his opening tee shot out of bounds and found water three times in a three-over-par 75.

Day leads on six under, one clear of five players, including fellow Australian Adam Scott who is bidding for a third successive PGA Tour win.

Englishmen Justin Rose and Paul Casey are in early contention on four under.

They are among 10 players within two shots of PGA Championship winner Day, who only needed one putt on each of his last seven holes as he played the back nine in five-under 31.

The world number three's lead could have been bigger but a wild drive out of bounds on the ninth led to a double bogey, however he was content with his opening round.

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

His compatriot Scott is aiming to become only the third player in 10 years - after McIlroy and Tiger Woods - to win three straight PGA Tour events.

Scott, who has had to change his putting style after anchored putters were outlawed at the start of this year, knocked in four par-saving putts - two from five feet, one from 10 and another from 12 in his 67.

"I didn't play my best golf tee to green, but I chipped and putted really well," he said.