Harman's impressive display saw him finish the day five shots clear of the field, with England's Tommy Fleetwood and Austria's Sepp Straka a further stroke back.
Harman's dominant round saw him land a barrage of birdies on his front nine, before eagling the 18th to finish with a score of 10 under.
Fleetwood, who was one of three players to shoot a 66 in the first round, struggled to make inroads into Harman's lead, eventually signing for a 71 to sit on five under.
Straka, meanwhile, emerged as a weekend contender with a sizzling back nine that included six birdies and a 67.
American Jordan Spieth, the 2017 champion, had a day of hard graft, struggling on the back nine and ending up going nowhere with a level-par 71.
The majority of the field found the going tough, with only 24 players under par after two rounds.
Harman's performance was made all the more impressive by his red-hot putter, which he rode through the first two rounds.
He got on a roll with birdies at the second, third, and fourth, and almost chipped in for an eagle on the fifth.
Harman kept the momentum on the back nine with a sensational chip-in from off the green at the par-four 12th, and a brilliant approach to the par-five 18th to seal his eagle putt.
He needed only 23 putts for his round, and if his stroke remains as steady over the weekend, he will be tough to catch.
As the field prepares for the third round, Harman leads the way on 10 under, with Fleetwood and Straka a further shot back.
With heavy rain forecast for the weekend, the golfers will face a different challenge, but Harman will be confident of maintaining his form and challenging for the Claret Jug.
The second round of the U.S. Open was played on Friday at the Pebble Beach Golf Links in California, with a mix of tough conditions and high-quality golf on display.
The course was set up to be extremely difficult, with multiple players commenting on how challenging the greens were.
Despite the difficulty, several players were able to post impressive scores, including world number one Scottie Scheffler, who shot a one-under 69 to sit at three under for the tournament.
Jon Rahm, the Masters champion, also had a strong round, carding a one-under 70 to sit at two over for the tournament.
U.S. Open champion Wyndham Clark also made the weekend with a gritty one-under 70, putting him at one-under for the tournament.
Defending champion Cameron Smith also had a strong round, eagling the 18th hole to make the cut at two-over.
Unfortunately, several former Open champions will be missing at the weekend, including Phil Mickelson, Shane Lowry, Collin Morikawa, and Francesco Molinari.
Australia's Travis Smyth had the loudest roar of the day, acing the 17th hole, but with an eight-over-par score, he will miss the weekend.
Overall, the second round of the U.S. Open demonstrated the extreme difficulty of the course, with only a few players able to post impressive scores.
The third round is set to begin on Saturday, with players fighting to make the cut and continue their pursuit of the championship.
LONDON DAILY ARCHIVE
Brian Harman Takes Control at the 151st Open Championship at Royal Liverpool Golf Club
American golfer Brian Harman has taken control of the 151st Open Championship at the Royal Liverpool Golf Club in Hoylake, England, after posting a six-under 65 in the second round.
22 July 2023 · 02:37 UTC
