Rafa Cabrera Bello marked his Arnold Palmer Invitational debut with a superb opening 65 which earned him a two-stroke lead over a heavyweight field at Bay Hill.
Cabrera Bello took advantage of the friendlier, early conditions and carded eight birdies to set the early clubhouse target at seven under par, and that score did not come under threat throughout the remainder of day one as the later starters had to deal with a firmer, faster course.
Graeme McDowell boosted his chances of claiming one of the three places on offer for The 148th Open as he fired an encouraging 68 to end the round tied for third with Phil Mickelson and Bubba Watson, but Rory McIlroy's title defence began in wayward fashion and he needed two late birdies to salvage a level-par 72.
But the star of the opening round was undoubtedly Cabrera Bello, who defied his lack of experience at Bay Hill and peppered the pins early and often, making four birdies over his first six holes before suffering his only setback at the first, where a bunkered drive led to a bogey.
However, the Spaniard's response was instant as he came within inches of an ace at the second before he drained 30-foot birdie putts at four and five and picked up another shot at the long sixth to race three clear of the field at the time.
The 34-year-old negotiated his final three holes in pars to stay at seven under, while Keegan Bradley emerged as his closest challenger when he reeled off three consecutive birdies late in his round and returned a bogey-free 67.
McDowell, who is fiercely determined to make the field for the final major of the year at his home course of Royal Portush, produced an impressive fightback from two early bogeys and birdied three of the next five to get under the card, and he started the back-nine with an excellent 20-foot putt for another gain at the 10th.
The former US Open champion then drilled a superb second to 15 feet at the long 16th and rattled in the putt for an eagle that lifted him to four under, and his 68 was matched by the American quartet of Watson, Mickelson, Patrick Rodgers and Billy Horschel.
Mickelson cruised to the turn in 33 but then attempted one of the most bizarre shots of his career following a blocked tee shot at the 10th that came within an inch or two of going out-of-bounds, his ball settling under a netted fence and left him looking likely to have to take a penalty drop.
But he opted to attempt to hack his ball back into play despite having to hit the shot right-handed while standing out-of-bounds, and the move backfired when his ball became entangled in the netting and dropped the wrong side of the OB line.
Mickelson eventually ran up a double-bogey six, but he regrouped and birdied 13 and 16 before his sensational 166-yard approach to the last pulled up barely a foot from the hole.
Reigning Open champion Francesco Molinari recorded his second hole-in-one on the PGA Tour at the seventh as he fired a 69 along with Tommy Fleetwood, whose fellow Englishmen, Matt Fitzpatrick and Tyrrell Hatton, were one stroke further back.
Justin Rose's bid to regain the world No 1 ranking from Dustin Johnson commenced with a solid 71 in his first outing for four weeks, while McIlroy littered his card with four bogeys as he endured an inconsistent day with all parts of his game.
The holder made a huge mistake at the 13th when his wedge from 92 yards spun into the water hazard, and he had to take a penalty drop for an unplayable lie two holes later and the resulting bogey saw him slip to two over.
But McIlroy came close to chipping in for eagle at 16 and then holed from 20 feet for a rare birdie at the tough, par-three 17th before a cast-iron par at the last ensured he remained seven shots behind the leader heading into day two.