Martin Kaymer insisted a second major title in the 114th US Open was not "a done deal" despite his dominant performance evoking memories of Rory McIlroy's runaway victory in 2011.
Kaymer said after his opening 65 - the lowest score ever in the US Open at Pinehurst - that no-one should expect him to do it again, but that was precisely what he did on Friday to set another record.
The 29-year-old's halfway total of 130 eclipsed the previous championship best of 131 set by McIlroy at Congressional, although McIlroy was 11-under and Kaymer 'only' 10 under after 11 birdies and just one bogey over the first two days.
It also equalled the lowest halfway total in any major championship, set by Nick Faldo in the Open at Muirfield in 1992 and matched by Brandt Snedeker in the same event at Royal Lytham 20 years later.
Eight shots clear when he signed his card, Kaymer eventually had to settle for a six-shot lead over American Brendon Todd - who shot a flawless 67 - which equalled the US Open record set by Tiger Woods in 2000 and matched by McIlroy three years ago.
"It's not a done deal," insisted Kaymer, who joined McIlroy as the only players to get to double digits under par in the first two rounds. "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.
"I played Congressional (finishing joint 12th) and I thought how can you shoot that low? And that's probably what a lot of other people think about me right now. But it will be quite interesting to talk to Rory about it, how he felt.
"It's not like we play different golf courses or easier golf courses, I'm sure he must have played so solid without making many mistakes and that I think is the main thing in majors, that you avoid the big numbers."
Kaymer became just the fourth European winner of the Players Championship in 41 years last month and considers his wire-to-wire victory at Sawgrass a second major title.
"It's a career goal to win one major," he added. "Fortunately, I got that done fairly early in my career (aged 25 in the 2010 US PGA). But I really believe at the end of your career it comes down to the big, huge moments where you could handle the challenges. It comes down to winning majors, World Golf Championship events, being on the Ryder Cup team, those things.
"Obviously if I could win a second, third, fourth major, whatever it's going to be, it would be very, very satisfying."
Asked on Wednesday what score he would be happy with after four rounds, Kaymer had said eight over par, but birdies on the 10th, 13th and 16th on Friday - having started from the 10th - took him to eight under after just 25 holes.
The tee on the par-four third had been moved forward and Kaymer took full advantage, driving the green from 315 yards and two-putting for his fourth birdie of the day.
Another soon followed on the fifth and despite a number of mis-hit iron shots on the closing stretch, Kaymer kept a bogey off his card to leave the chasing pack facing a monumental task to deny him a second major title.
His first came at Whistling Straits in 2010, when Johnson was famously denied a place in the play-off between Kaymer and Bubba Watson due to a two-shot penalty on the 72nd hole, the 29-year-old grounding his club in a bunker that he thought was a waste area.
Speaking after carding his second consecutive 69 to lie joint fifth a shot behind Kevin Na and Brandt Snedeker, Johnson said: "I would have taken it on Wednesday. And no, I wouldn't have thought it would be eight shots behind."
Sweden's Henrik Stenson birdied three of his last five holes to shoot a 69 and join Johnson on two under, with McIlroy one under after a 68 and world number one Adam Scott level par thanks to a 67.
Defending champion Justin Rose was one over, alongside compatriot Danny Willett, after a 69 but said: "I still feel like I am in the tournament. Over 72 holes everyone is going to have a rough patch and Martin shooting 65, 65 hasn't had one yet.
"Ten under here is unbelievable golf. Take Martin out and there is a great tournament going on at this stage."
Graeme McDowell, joint second overnight, struggled to a 74 to fall back to two over, while teenage amateur Matt Fitzpatrick continued to impress in his last event before turning professional.
Playing alongside Rose and Open champion Phil Mickelson, the 19-year-old from Sheffield added a 73 to his opening 71 and was the only amateur to make the cut on four over, with six-time runner-up Mickelson just a shot better off after also shooting 73.