Bryson DeChambeau said his swing fix "came to him" in a dream after the US. Open champion kept his title defence alive.
DeChambeau opened his bid for back-to-back US Open trophies with a 73 but the big-hitting American responded by posting a two-under-par 69 on Friday.
An eagle, four birdies and four bogeys saw DeChambeau surge 47 positions on day two, moving within five shots of co-leaders Richard Bland and Russell Henley at Torrey Pines.
Reflecting on his bounce-back display heading into the weekend, DeChambeau credited a late-night tweak.
"I was sleeping and it came to me in the middle of the night," DeChambeau told reporters.
"Woke up and I was like, hmm, I'm going to try this, and my intuition is pretty good, so I went out and tried it and it worked, just keeping the right wrist bent for a lot longer through impact."
"It's more just my intuition telling me there's something weird here, what's going on, and I couldn't figure it out for an hour and a half last night, an hour last night," said DeChambeau said.
"Going back and just sitting down, eating dinner and just thinking about it, thinking about it, I literally won't talk to anybody for like an hour, just thinking, thinking, thinking, and sure enough, I went to bed and I found a little something that worked for my driver."
DeChambeau added: "I feel like if I can clean up my iron play and get a little more comfortable with the irons and the drivers, I'll have a good chance for this weekend."
He is tied for 13th alongside the likes of rival Brooks Koepka (73), Justin Thomas (69) and Collin Morikawa (67).
Amid their ongoing feud, DeChambeau and two-time U.S. Open champion Koepka narrowly avoided being paired together for Saturday's penultimate round.
Koepka – eyeing a fifth major crown – lost ground on the leaders after mixing five bogeys and just three birdies but he told reporters: "I feel right there. I feel like I'm in it. Just need to put two solid good rounds and put the ball in the fairway, and that's it.
"I love the way I'm putting. I love the way I'm striking it. Just need to keep doing it."
Four-time major winner and former world number one Rory McIlroy is a stroke further back following his second-round 73.
"A bit of a rollercoaster, got off to a good start," McIlroy said. "Made a couple of birdies early on and was under par for the round.
"Then I made a couple of mental errors and missed it in the wrong spots, and when you do that around this golf course, it's just really hard to see a par.
"I made a few bogeys, but birdieing two of the last four holes definitely makes me feel better about the round and gives me a nice bit of momentum going into tomorrow.
"So yeah, in for the weekend and still feel like I've got a really good chance."
US PGA Championship winner Phil Mickelson also feels he can "make a run at it" after avoiding the cut on Friday.