Dustin Johnson fired a seven-under 64 to climb into a share of the Pebble Beach Pro-Am lead after the second round.
The world number one made eight birdies on the Monterey Peninsula Country Club course to move into 12 under in Pebble Beach, California, on Friday.
A two-time winner of the PGA Tour event, Johnson started on the back nine and holed five birdies, before three in four helped him into the lead.
Johnson has made a fine start to this year, winning the Tournament of Champions before a top-10 finish at the Abu Dhabi HSBC Championship.
Joining him atop the leaderboard is fellow American Beau Hossler, who carded a five-under 67 on the Spyglass Hill Golf Course.
Hossler backed up his opening-round 65 with a bogey-free Friday.
Troy Merritt (67 on Spyglass Hill) and Julian Suri (67 on Monterey Peninsula) are two shots back in a tie for third.
A further shot adrift are the likes of four-time champion Phil Mickelson, Spaniard Jon Rahm and Australian Jason Day.
Rahm, the in-form world number two, carded a second straight 67 to be in the six-man group at nine under.
Day and Mickelson fired six-under 65s on Monterey Peninsula, with Aaron Wise, Kevin Streelman and Steve Stricker joining the group in a tie for fifth.
Defending champion Jordan Spieth managed to get going, shooting a five-under 66 on Monterey Peninsula to be tied for 23rd.
Making his first PGA Tour appearance of the season, Rory McIlroy struggled on the same course.
The Northern Irish four-time major champion carded a 74 to slip back to one under as he endured a forgettable few moments on the par-four fifth hole.
McIlroy had an eagle putt at the hole, but left with a double bogey after an implosion, before two more bogeys followed to finish his round.
21. Oktober 2018
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|Allegri: Juventus abandoned Genoa clash|
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|Valverde accepts Barcelona will miss Messi|
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|Barcelona have not won a Clasico without Messi since his debut|
|Ramos calls for Real Madrid unity after latest loss piles pressure on Lopetegui|
|Hamilton has title in sights after storming to Austin pole|
|Inter, El Clasico and more - the games Messi will miss with broken arm|
20. Oktober 2018
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|Messi out of Clasico with fractured arm|
|Awesome Ashton marks Sale bow with hat-trick|
|Klopp hopes for positive Henderson prognosis amid Liverpool injury issues|
|Benitez ´convinced´ Newcastle can survive despite seventh defeat|
|Barcelona 4 Sevilla 2: Messi injured but champions go top|
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|Leicester City defender Chilwell signs new six-year contract|
|PSG´s Tuchel hopes Verratti and Di Maria can face Napoli|
|Liverpool star Salah had no fear during scoring drought|
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|Barca concern as Messi substituted with worrying arm injury|
|Howe: South coast derby draw a fair result|
|Our heads were in Manchester – Allegri left fuming at Juventus´ loss of focus|
|Derby County 2 Sheffield United 1: Marriott blunts Blades with 77th-minute winner|
|We have so many problems – Jokanovic alarmed by Fulham defensive woes|
|Huddersfield Town 0 Liverpool 1: Salah snaps winless streak|
|Pellegrini ruing injuries after Yarmolenko hurts ankle|
|Villarreal 1 Atletico Madrid 1: Simeone´s side denied LaLiga top spot|
|Gracia: Not easy to dominate Wolves like that|
|Isner´s Finals hopes hindered by Stockholm defeat|
|Dyche incredulous at refereeing decisions in Man City thrashing|
|Juventus 1 Genoa 1: Champions´ winning run ends despite record Ronaldo goal|
|´Fantastic´ Lamela urged to find consistency by Pochettino|
|You don´t want to lose any players - Young speaks out on Wade NFL speculation|
|Championship Review: Smith gets off to a winning start, Leeds beaten|
|Guardiola hails extraordinary Fernandinho after Burnley drubbing|
|Pochettino lauds Lloris as one of world´s best after West Ham heroics|
|Paris Saint-Germain 5 Amiens 0: Ten wins in a row for PSG as Neymar rests|
|Cristiano Ronaldo nets record 400th league goal|
|Marcelo backing beleaguered Lopetegui despite Madrid slump|
|Garcia dazzles to hit the front at shortened Valderrama Masters|
|Cardiff City 4 Fulham 2: Paterson gets Bluebirds off the mark|
|Newcastle United 0 Brighton and Hove Albion 1: Benitez´s men bottom after dismal defeat|
|West Ham 0 Tottenham 1: In-form Lamela settles London derby|
|Manchester City 5 Burnley 0: De Bruyne returns in comfortable win|
|Wolves 0 Watford 2: Capoue and Pereyra turn form book on its head|
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|Prove you´re crazy about Inter - Spalletti rallies players ahead of Milan derby|
|Wolfsburg 1 Bayern Munich 3: Lewandowski leads Kovac out of trouble|
|Goerges betters Bencic to clinch Luxembourg title|
|Morgan wants more from ´rusty´ England despite series win|
|Sarri says sorry after touchline bust-up overshadows Chelsea´s late escape|