Clark had a four-shot lead slashed in half after returning to Shinnecock Hills early on Friday morning to conclude his weather-delayed first round but he then wrestled back control.
The 2023 winner followed up his opening 64 with a second-round 69 to move to seven under and open a four-stroke lead over fellow American Xander Schauffele (71-66) and England's Matt Fitzpatrick (67-70).
Clark was last year embroiled in controversy when caught destroying multiple lockers after missing the halfway cut at brutal Oakmont Country Club.
But the 32-year-old has been a picture of calm and control in separating himself from the field so far this week.
"I've gotten a lot of grief since last year -- rightfully so," Clark said.
"The thing that's unfortunate is that's not who I am, what happened last year.
"I'm hoping I can win back the fans that I had, or some new fans, because it was a terrible incident.
"I really feel like I can show people that I'm fun and outgoing. I'm fierce, competitive, love the game, respect the game, and I just had a bad moment."
While well in charge, Clark will need to retain his nerve over what will surely be a testing weekend as he tries to fend off a swathe of serial major winners hunting him down.
As well as two-time major champ Schauffele and in-form 2022 US Open champ Fitzpatrick, has several other heavyweights in pursuit.
Dual major winner Collin Morikawa surged to two under to be in a tie for fourth with a sizzling second-round 65 while Justin Thomas (71) is one shot further back.
Rory McIlroy and Brian Harman were also in red numbers early in their second rounds.
But Clark presumably won't have to worry any longer about Dustin Johnson after the former world No.1 and the leader's closest first-round challenger endured a dramatic day-two collapse.
A winner at in Oakmont in 2016, Johnson rolled back the years to post an opening 66 after finishing with two late birdies to briefly reduce Clark's lead to two shots.
Johnson remained at four under through 10 holes of round two but the former US Open and Masters champion then dropped eight shots in four holes, including a quadruple-bogey eight on the 15th, to plummet to three over with a second-round 77.
Australia's challenge was still being led by Adam Scott, on his landmark 100th consecutive major appearance, with an opening three-over-par 73.
Scott started his second round with a bogey and, like compatriots Min Woo Lee (74), Lucas Herbert (74) and Cameron Smith (75), he had a battle on his hands to make the cut.
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