Argentina's Emiliano Grillo and England's Matt Fitzpatrick are the joint-leaders after the first round of the Arnold Palmer Invitational in Florida.
Grillo, the 2016 PGA Tour Rookie of the Year, birdied five of the first 11 holes and two of the last three en route to his five-under 67.
Fitzpatrick went through bogey-free in the opening round of the event, the first since Palmer's death in September.
Paul Casey and American duo Lucas Glover and Charley Hoffman are tied for third, one shot back.
Florida-born Australian Ryan Ruffels, 18, and compatriot Greg Chalmers are at three under.
In unusually cool conditions at Bay Hill, defending champion Jason Day posted a two-under 70.
Making a much poorer start was Rory McIlroy, the four-time major champion producing a rollercoaster back nine to card a two-over 74.
The Northern Irishman was one under through nine, but he bogeyed the 10th before finding a bunker and water at the next for a double bogey.
He had birdies at 13 and 16, but bogeys at 15 and 18 saw him end up in a tie for 58th.Cody Gribble, who had a forgettable five-over 77, produced one of the moments of the day, nudging an alligator back into the water.
Don't try this at home.— PGA TOUR (@PGATOUR) March 16, 2017
Sharing 58th place with McIlroy is Palmer's grandson, Sam Saunders.
The "shot" of the day.— PGA TOUR (@PGATOUR) March 16, 2017
Saunders tees off with Arnie's cart in the foreground. pic.twitter.com/NBjdzzjcoA
Reigning Masters champion Danny Willett, meanwhile, was a late withdrawal due to illness.
20 de noviembre 2017
|Hansen hails All Blacks progress|
|Kohli´s record century precedes Bhuvneshwar heroics, but Sri Lanka cling on|
|Shape up! Heynckes reveals demand to Bayern star Vidal|
|Australia hope to open England ´scars´ in Brisbane|
|Smiling Broad sports bruise after golfing mishap|
|Ramos sits out Madrid trip to APOEL|
|West Brom sack Pulis after wretched run|
|Ball fighting fit ahead of Ashes opener at the Gabba|
|Murray should appoint Delgado as Lendl replacement - Henman|
|Former Wimbledon champion Novotna dies aged 49|
|Lloris wants Spurs to forget title and focus on top four|
|Pogba no Gerrard yet, says Benitez|
|Pearce released from Roosters contract|
|Expect to get six ducks – Paine reveals Rogers´ Ashes advice|
|Lyon: I don´t care if Stokes plays Ashes|
|Curry´s offensive explosion leads Warriors past Nets|
|Ball records second triple-double to join Magic, West in record books|
|Patriots, Ravens win among multiple blowouts|
|Flyers´ Gudas suspended for 10 games for violent slash|
|Two-time NBA All-Star David Lee announces retirement|
|Guardiola will ´kill´ City stars if they get complacent|
|Bills coach McDermott to ´evaluate´ quarterback position|
|LeBron on Kaepernick controversy: I don´t respect the NFL|
|Ibrahimovic: My injury was worse than people know|
|Russell to leave Warriors at end of season|
|Cook cruises to first PGA Tour win|
|Truex wins first NASCAR championship|
|Cardinals´ Fitzgerald now fifth all-time in receiving yards|
|Icardi like a ´raptor pouncing on its prey´, says Spalletti|
19 de noviembre 2017
|Tired Goffin insists: ´I will be ready for Davis Cup final´|
|In-form Chelsea have regained hunger - Conte|
|Stones can bounce back stronger - Kompany|
|Guardiola ready to risk Kompany for Man City after Stones´ injury|
|City style suits me and thrills neutrals, says De Bruyne|
|Dimitrov thanks Scherzinger for giving him the X Factor at ATP Finals|
|Inter 2 Atalanta 0: Icardi brace sends Spalletti´s side second|
|Giampaolo promises more from ´extraordinary´ Sampdoria|
|Dimitrov overcomes gutsy Goffin to win ATP Finals|
|Memorable Ashes Moments: Australia skittled for 98 at MCG|
|NFL extends deal to play in Mexico through 2021|
|Record-breaking Valencia tee up blockbuster Barcelona clash|
|Poor West Ham performance at Watford was to be expected - Moyes|
|We will see what happens in the future - Silva non-committal on Everton rumours|
|Stones can bounce back stronger - Kompany|
|Racing climb above Toulon in thriller|
|Football needs to do more to combat racism - Boateng|
|Watford 2 West Ham 0: Misery for Moyes on Hammers bow|
|Unlucky 13: Benevento suffer record-breaking defeat|
|Juventus lost composure amid Sampdoria onslaught - Allegri|
|Exeter capitalise on Saracens defeat to top Premiership|
|Race to Dubai winner Fleetwood hails ´biggest day of my career´|
|Dutch Grand Prix a ´realistic´ prospect from 2020|
|Sampdoria 3 Juventus 2: Champions slip further off the pace after thriller|
|Coleman confirmed as Sunderland boss|
|I was just injured - Belgium´s Nainggolan blasts ´stupid´ claims of feigned ailment|
|Leeds United 2 Middlesbrough 1: Losing streak snapped to ease pressure on Christiansen|
|Ioane and Romano to miss All Blacks´ Wales clash|
|One punch only! Tete retains world title with 11-second knockout|
|Hughes backs Giggs for Wales job|
|Bennett: Social media clip prompted Brown withdrawal|
|Memorable Ashes Moments: Anderson and Panesar defy Australia in Cardiff|
|Madrid confirm Ramos´ broken nose after derby clash|
|Kane wants to retire with Tottenham|
|Mourinho: Man United lacked balance with attacking line-up|
|Fleetwood wins Race to Dubai after Rose wilts, Rahm claims tournament win|
|Pastore not considering PSG exit to help World Cup chances|
|Wenger, Ozil & Sanchez uncertainty affecting Arsenal, says Seaman|
|Dhawan, Rahul lead India revival in Kolkata|
|Silva not surprised by Chelsea, Spurs interest in Richarlison|
|Ancelotti, Conte, Allegri on shortlist to replace Ventura|