Ludvig Aberg, trying to become the first US Open debut winner since 1913, carried a one-stroke lead into Saturday's third round at Pinehurst, where top-ranked Scottie Scheffler was 11 strokes adrift.
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Sweden's sixth-ranked Aberg stood on five-under 135 as he awaited a 3:35 p.m. (1935 GMT) start alongside 2020 US Open winner Bryson DeChambeau.
After a runner-up effort in last month's PGA Championship, DeChambeau was among eight of 12 LIV Golf starters among the 74 players who made the cut for the weekend.
Also one stroke off the pace with DeChambeau on 136 were ninth-ranked American Patrick Cantlay and Belgium's Thomas Detry.
Four-time major winner Rory McIlroy of Northern Ireland was another shot back on 137 with American Tony Finau and France's Matthieu Pavon.
The winner takes $4.3 million and the runner-up a hefty $2.32 million from the record $21.5 million purse.
But Aberg, runner-up at April's Masters in his major debut, could carry off a bit of history as well.
Not since 20-year-old American amateur Francis Ouimet upset Britain's Harry Vardon and Ted Ray at The Country Club in his hometown of Brookline, Massachusetts, some 111 years ago has a player won the US Open in his debut.
Aberg is the first debut player since Taiwan's Chen Tze-chung in 1985 to lead the US Open after 36 holes.
The 24-year-old Swede has triumphs on the US PGA Tour and DP World Tour since turning professional a year ago.
A major reason for his lead at punishing Pinehurst, with its dome-shaped elevated greens and dirt and weeds waste areas, is that he leads all players in both driving accuracy at 93 per cent and greens in regulation at 83 per cent, mainly avoiding the course's two major danger zones.
The best any Swedish player has done in a US Open is fourth, a feat managed by Niclas Fasth, Robert Karlson and Henrik Stenson.
World No 1 Scheffler, the hottest golfer entering the week and a huge favourite, was six-over and 11 strokes back after a bogey at the par-4 fourth, finding native area left off the tee.
Scheffler made the cut on the number following a 74 on Friday but was 1-over after seven holes on Saturday.
Scheffler was the first player since Tom Watson in 1980 to win five US PGA Tour events before the US Open, taking the fifth last week at the Memorial, and has 12 top-10 finishes in 13 events this season.
The usually stoic and calm Scheffler, however, could feel the frustration at Pinehurst's unique challenge, flipping his putter in the air and letting it fall after one near miss Friday and also slamming down his driver after a woefully errant tee shot.
Cantlay, in his best spot after 36 holes in 30 major starts, has a chance to move past Collin Morikawa for the final spot on the US team for the Paris Olympics but needs no worse than a two-way share of second to do it. Four other Americans must win to make the squad for France.