Leader Adam Hadwin was set for a morning start as Friday's second round of the US Open began while Rory McIlroy and defending champion Jon Rahm could have to face afternoon thunderstorms. Canada's Hadwin opened Thursday at The Country Club with a four-under par 66, his lowest career round at a major, to grab a one-stroke lead over third-ranked McIlroy and four others after 18 holes. Hadwin, the first Canadian to lead a US Open since Mike Weir in 2009, has never been better than 24th in 19 prior major starts but he hopes for more success when he starts at 8:24 a.m. (1224 GMT) off the 10th tee.
"Pick a target. Have a number in mind and try and execute. Go find it and hit it again," Hadwin said of his second-round strategy over the 7,254-yard layout.
"I've done a great job with that over the last little bit. It's getting easier as I continue to play better to keep in that mindset.
"There's a lot of golf left and this course is only going to get tougher."
Hadwin made it into the field as an alternate when England's Paul Casey withdrew last week due to a back injury.
England's Callum Tarren, Sweden's David Lingmerth, American Joel Dahmen and South African M.J. Daffue -- with only 19 major starts between them -- joined four-time major winner McIlroy in second on 67.
Daffue, in his major debut, wasn't even planning to try and qualify for the event before he clinched a PGA Tour spot. Now he's the earliest starter among top chasers, out in the second group off the first tee.
"Sometimes you have to go this way to end up in the right place," said Daffue. "I'm really glad. I'm enjoying everything about it."
Scattered storms and gusty winds are expected in the area when McIlroy and second-ranked Rahm are due to tee off in the early afternoon.
Any delay likely means the cut won't be made until Saturday and would set up a hectic charge for the field to try and finish 72 holes by sunset Sunday.
McIlroy, chasing his first major title since 2014, comes off a victory in last week's PGA Canadian Open. Not since 1934 has a player won the week before and then captured the US Open.
The 33-year-old from Northern Ireland produced his 29th major round in the 60s on Thursday. When he has opened majors with back-to-back rounds in the 60s, McIlroy has won three times.
Top-ranked Masters champion Scottie Scheffler, trying to match Tiger Woods as the only world number ones to win a US Open, started with a 70.
DJ's 68 is LIV's best
England's Matt Fitapatrick, sitting two adrift on 68, won the 2013 US Amateur at The Country Club. The only player to win a US Open and US Amateur at the same venue was Jack Nicklaus at Pebble Beach.
Also on 68 with morning starts were England's Justin Rose, the 2013 US Open champion, and American Dustin Johnson, the 2016 US Open and 2020 Masters champion.
Johnson had the lowest score among the 15 LIV Golf players in the field of 156, a group that went a combined 53-over par in the opening round of its first event against US PGA Tour talent.
With the richest purses in golf history, Saudi-backed LIV Golf has lured players from the PGA Tour, which banned 17 current and former members from its events last week after they played LIV's debut event in England.
A regular-season LIV event offers $25 million in prize money, $7.5 million more than the US Open pays.
The US Golf Association decided to stay with its qualifying criteria and didn't ban LIV Golf players for this week, but USGA chief executive Mike Whan warned such a move was possible in the future.
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