Graeme McDowell began his challenge at the Arnold Palmer Invitational with a four under 68.
The 2010 US Open champion, a two-time runner up at Bay Hill, carded an eagle, four birdies and two bogeys in Florida.
The highlight of his round was that eagle on the par five sixth when he rolled in a putt of some 75 feet.
McDowell’s solid opening effort left him six shots behind the leader Adam Scott who equalled the course record at Bay Hill with a stunning 62.
Scott carded two eagles, seven birdies and one bogey to set a daunting clubhouse target of 10 under par, matching the course record shared by Andy Bean (1981) and fellow Australian Greg Norman (1984).
“Obviously I’m really thrilled with the start,” said Scott, who is closing in on Tiger Woods at the top of the world rankings ahead of his US Masters defence in three weeks’ time.
“It’s maybe a little surprising. I don’t know where it came from, but the putter certainly got hot.”
Scott is making his first appearance at Bay Hill since 2009. He missed the cut in his last two starts and his only top-10 finish in six previous appearances came in 2004, when he tied for third.
“I just had a few frustrating years here and left it off the schedule,” Scott told reporters after his round.
“Coming back fresh was obviously a good thing.
“But I like the changes they’ve made since the time I have not been here. And today was just one of those days where the hole was a bit like a bucket.”
The reigning Masters champion started on the 10th and birdied his opening hole before picking up another shot on the par-five 12th after getting up and down from a greenside bunker.
Scott then holed from 25ft on the 14th and from a similar distance off the green on the next, before continuing his hot putting steak by making an eagle from 35ft on the par-five 16th.
His solitary bogey came from an errant approach to the 18th, but the 33-year-old bounced back quickly with a birdie from close range on the third and another eagle from 20ft on the fourth.
Further birdies on the sixth and seventh meant matching front and back nines of 31 and left Scott three ahead of Japan’s Ryo Ishikawa and America’s John Merrick.
Padraig Harrington carded an opening round 70, while Darren Clarke finished on three over 75.
Scott’s predecessor as Masters champion, Bubba Watson, withdrew after an opening 83 citing allergy problems. Scott cannot overhaul the absent Woods - the defending champion pulled out on Tuesday with on-going back problems.
- with a victory on Sunday, but would claim top spot before his Masters defence if both players did not play again before the year’s first major at Augusta.