Martin Kaymer will take a six-shot lead into the third round with the best 36-hole score in US Open history.
The 29-year-old German, the 2010 US PGA champion, fired a second straight 65 to set the pace at 10 under at Pinehurst.
Kaymer led by eight before Brendon Todd hit 67 to climb to four under and fellow Americans Kevin Na (69) and Brandt Snedeker (68) went three under.
Rory McIlroy ended one under after a 68, while six-time runner-up Phil Mickelson took 73 to slip three over.
Defending champion Justin Rose inched to one over after a 69 and world number one Adam Scott made progress with a 67 to move to level par.
But Kaymer was in imperious form as he reached halfway in 130 shots to eclipse McIlroy's record mark of 131 when he won the US Open at Congressional in 2011.
He also equalled the best 36-hole mark at any major championship, set by Nick Faldo in the 1992 Open at Muirfield and Snedeker at Royal Lytham in 2012.
His margin matches the largest halfway lead at the US Open, set by Tiger Woods at Pebble Beach in 2000 and McIlroy three years ago. Woods ended up winning by 15 shots and McIlroy won by eight.
Former world number one Kaymer, who won the prestigious Players Championship in May, took advantage of morning greens softened by heavy overnight rain to pile up three birdies on his front nine, including a 25ft effort on the short 16th, after starting from the 10th.
He then picked up further shots at the third and fifth before missing a putt from 10ft for a 64 on the last.
"It's not a done deal," said Kaymer, who holed the winning putt for Europe in the Ryder Cup at Medinah in 2012. "You don't approach Saturday and Sunday in a relaxed way.
"It's never a time when you can relax, unless it's Sunday afternoon and you are raising the trophy. There's never a time you can take it easy, you have to set your own goals and keep playing well."
World number two Henrik Stenson of Sweden, Zimbabwe's Brendon de Jonge and Americans Brooks Koepka, Dustin Johnson and Keegan Bradley all finished two under.
Northern Ireland's McIlroy kept alive his bid for a second US Open title and third major with three birdies and one bogey, while countryman Graeme McDowell, the 2010 champion who shared second overnight, dropped back with a four-over 74 to end two over.
"What Martin has done over the first couple of days has made one under par look pretty average," said McIlroy, 25. "If he can hold on to that 10-under total, he's going to win this tournament."
Five-time major champion Mickelson admitted he was "not overly optimistic" about his chances of winning a first US Open this week to complete a carer Grand Slam of all four major titles.
The Open champion would join fellow Americans Gene Sarazen, Ben Hogan, Jack Nicklaus and Tiger Woods and South African Gary Player as the only men to have achieved the feat.
"The hole looks like a thimble right now," said Mickelson, 43. "I'm having a hard time finding it.
"I'm not going to give up but I need to shoot six or seven-under to have a realistic chance."
The 33-year-old Rose, bidding to make the first successful defence since Curtis Strange in 1989, bogeyed the last but remained upbeat.
"I still feel like I am in the tournament," said Rose, who pipped Mickelson to clinch his maiden major in the US Open at Merion last year.
"Over 72 holes everyone is going to have a rough patch and Martin shooting 65, 65 hasn't had one yet."
Rose's amateur playing partner Matthew Fitzpatrick, 19, took 73 to finish four over, while fellow Englishman Ian Poulter carded a second straight round of 70 to maintain station at level par as he chases a first major title.
But former world number ones Luke Donald (+6) and Lee Westwood (+8) and two-time Masters champion Bubba Watson (+6) all missed the cut, which fell at six over.
Wales' Jamie Donaldson finished 11 over after an 81 which included a two-shot penalty when he and playing partner Hunter Mahan hit each other's golf balls on the 18th fairway.