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.
22. Oktober 2017
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|Klopp slams Lovren: I would have stopped Kane getting the ball!|
|Udinese 2 Juventus 6: Khedira hat-trick inspires Bianconeri rout|
|We could have scored more - Two-goal Kane hails ´unbelievable´ Tottenham|
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|Atletico needed win at Celta, says Simeone|
|Tottenham set Premier League attendance record|
|Tottenham 4 Liverpool 1: Kane double increases pressure on Klopp|
|Centurion Kohli surpasses Ponting but Latham and Taylor thwart India|
|Montella questions VAR, promises ´united´ Milan will deliver|
|Tsonga overcomes Schwartzman to claim Antwerp crown|
|Garcia edges out Luiten for another Valderrama victory|
|Celta Vigo 0 Atletico Madrid 1: Fit-again Gameiro ends visitors´ winless run|
|Du Plessis carried off but Proteas seal whitewash|
|Bishoo snares five as Windies turn tables on Zimbabwe|
|Wenger: Ozil back to his best for dominant Arsenal|
|Dolberg double sinks Feyenoord in De Klassieker|
|We´ve let him down – Keane backs Koeman after Arsenal capitulation|
|Ospreys´ Baldwin shows off gruesome lion bite injury|
|It´s not time to be crazy - Koeman calls for calm after Everton thumping|
|Mertesacker lauds compatriot Ozil after Everton thumping|
|AC Milan 0 Genoa 0: Bonucci sees red as 10-man Rossoneri fight for point|
|Guangzhou Evergrande claim seventh straight Chinese Super League crown|
|Everton 2 Arsenal 5: Koeman on the brink as hosts capitulate|
|Dzumhur wins again in Russia, Berankis eyes swift revenge|
|Dovizioso downplays early error´s importance|
|Muguruza survives late Ostapenko surge in Singapore|
|Ipswich Town 0 Norwich City 1: Maddison gives Canaries more derby glory|
|Gary Neville thinks he is done as a football manager|
|Marquez hoping for serene title tilt after Phillip Island fright|
|Ibrahimovic has ´minimum´ five or six years left, claims Raiola|
|Pliskova kickstarts WTA Finals with statement win over Venus|
|A-League Review: Vargas injury mars Newcastle Jets win, late winner gives Perth Glory first victory|
|Maybe the Premier League title race is already over - Klopp|
|Joshua frustrated with Pulev withdrawal|
|Rossi: I could have fought Marquez if not for crazy Iannone|
|Pochettino accuses Walker of ´alarming lack of respect´ over Tottenham exit|
|Folau won´t play until 2018 after Barbarians clash|
|Red-hot Thomas survives play-off to win The CJ Cup at Nine Bridges|
|Back-to-back titles loom for Marquez after winning Phillip Island thriller|
|Girardi unsure of Yankees future after Astros loss|
|Warriors, Cavs and Thunder lose as Rockets stay perfect|
|Astros blank Yankees to earn World Series showdown with Dodgers|
|Curry, Durant both ejected in final minute of Warriors´ loss to Grizzlies|
|Pochettino: Mourinho put Dier in compromising position amid United interest|
|Sarri: Napoli care more about Serie A than Champions League|
|Portis apologises for punching Bulls team-mate Mirotic|
|Vettel hails Ferrari pace as title hopeful aims to stop Hamilton|
|F1 title will have to wait unless Vettel makes silly mistake – Hamilton|
|My goal was legal against Malaga, insists Barca´s Deulofeu|
|Newcastle overcome Bordeaux as Edinburgh make history in Moscow|
|Valverde does ´not see any problem´ with Suarez´s sour substitution reaction|
|Hamilton dominates in Austin as title moves into view|
|Ignore the noise, says under-fire Ozil|
21. Oktober 2017
|It´s like playing against aliens - Inter´s Spalletti hails Napoli players after draw|
|PSG duo Alves and Lucas to miss Marseille clash|
|CAF Champions League Review: Wydad Casablanca book final berth|
|Saracens survive Ospreys scare, Clermont win marred by Lopez injury|
|Getting there - Murray posts positive update on comeback from injury|
|Napoli 0 Inter 0: Handanovic heroics put an end to Partenopei´s winning streak|
|Barcelona 2 Malaga 0: Controversial win sees hosts extend LaLiga lead|
|Kvyat set for showdown talks with Red Bull boss Marko|
|Weidenfeller to end Dortmund stay at end of season|
|Pellegrino wants patience from Southampton saviour Boufal|
|Sad day for democracy - Guardiola gives latest take on Catalan crisis|
|Heynckes awaiting news on Muller injury|
|It was a penalty - Silva hits back at Burnley boss Dyche|
|Hamburg 0 Bayern Munich 1: Tolisso sends Heynckes´ men joint-top|
|Southampton 1 West Brom 0: Boufal stunner ends Saints´ winless run|