Martin Kaymer took a giant stride towards his second major title as he fought his way round Pinehurst No.2's difficult set up to head into Sunday's final round five clear of Rickie Fowler and Eric Compton.
The German, who started the day six clear at the top, recovered from a worrying start that saw him bogey two of his first four holes to card a two-over par 72 - including a decisive birdie at 18, his only one of the day.
The American duo of Fowler and Compton were the most impressive on Saturday, however, as the USPGA sought to toughen up the a North Carolina course with pins described by legendary golfer Kenny Perry as "the toughest set of 18 he'd ever seen".
Both of them delivered three-under 67s to haul themselves to within five strokes of Kaymer's lead, but it will take some equally as special - if not more so - if either of them are to triumph over the German on Sunday night.
There still remains a host of top players in the chasing pack residing inside the top 10, but they face an incredibly tall order with the course not set to get any easier for the final round.
Defending champion has made a good fist of his first major title defence after his level-par 70 left him at one over for the tournament in a tie for 10th alongside America's Jordan Spieth.
One stroke ahead of them is a trio at level par that includes the widely tipped Matt Kuchar, while his compatriot Brandt Snedeker is one shot closer to Kaymer at minus one.
Lurking in the red at two under are world number two Henrik Stenson and Dustin Johnson - and with their length off the tee, it may well be this pairing that pose the biggest threat to Kaymer pulling off one of the most memorable wire-to-wire victories the US Open has ever seen.
His stunning successive 65s the previous two days may well have propelled him into a supreme position of strength, but the way he battled on Saturday was just as impressive, with many of the early starters being chewed up and spat out by Pinehurst.
Japan's Toru Tanuguchi had a particularly torrid time, carding an incredible 18-over par 88, to show just how tough the set up was.
And early in Kaymer's round, he appeared to be struggling. A bogey at the second clearly unsettled the German as an errant tee shot on four led to an unplayable lie.
However, the 2014 Players champion crucially wrestled the momentum back in his direction as he drained the 15-foot bogey putt he had left himself.
What followed on the next hole was quite incredible. After another errant tee shot saw him once again in among the waste land surrounding the fairways, he pulled off an unbelievable seven iron from 200 yards to five feet for eagle. The way he's performed on the greens this week, he was never missing the putt, and suddenly his lead was up to seven.
Another bogey immediately followed, though, but three pars leading up to the turn saw him turn in 36 - one shot better than the field average.
A similar wobble to the front nine followed though. He bogeyed 13 and 15 sloppily, while Fowler was coming home in 33 to firmly put himself into contention with the gap now just four.
But Kaymer's a major champion, and that experience counts for a lot on the biggest of occasions. He made his most important birdie of the week at his 54th hole and, as a result, another round anywhere near level par will see him become the fourth European winner of America's Open in the last five years.
It will be nothing short of deserved either. The 29-year-old has been a class above anyone else in Carolina this week, opening with statistically the two best rounds ever of a major championship.
If he becomes a double major winner before turning 30, those who wrote him off after his 2012 slump will begin to wonder just how much he can achieve in the game.