Jim Furyk was in sight of a second US Open title, nine years after his first, in the mist and drizzle at San Francisco's Olympic Club.
The 42-year-old American, showing all the grit and cool-headedness he is famed for, reached the turn in a gripping final round in 35 and that gave him a one-stroke lead over the field.
Furyk started the day sharing a two-stroke lead with Northern Ireland's Graeme McDowell, a player also seeking his second US Open title after his win at nearby Pebble Beach two years ago.
They started the day as the only two men under par at 209 and it soon became evident in the cold mist and spotty rain that staying at one-under could very well be enough to lift the trophy.
With Tiger Woods an early blowout after dropping six shots in six holes, Furyk moved clear for the first time when McDowell bogeyed the third following an overhit chip.
When the Ulsterman had another bogey at the fifth, Furyk was two clear of the field with two-time former winner Ernie Els of South Africa joining McDowell on one over after an eagle two at the short par-four seventh.
England's world No. 3 Lee Westwood saw his hopes of a first major badly hit when he lost his ball up a tree on the fifth and he had to settle for a double bogey.
Playing partner Fredrik Jacobson of Sweden, alone in second place overnight two strokes off the pace, had bogeys at the second, fifth and sixth.
Furyk narrowly missed a 10-foot putt that would have given him a three-stroke lead at the eighth, allowing a trio of young Americans - Michael Thompson, John Peterson and Webb Simpson - all playing ahead of him, to move into contention at two strokes off the lead alongside McDowell.
Simpson, a rising 26-year-old star from North Carolina who won two tournaments on the PGA Tour last year, then made it four birdies in five holes by sinking a four-footer at the 10th to cut the lead to just one stroke.
Furyk parred the ninth to stay in the lead as he reached the turn with McDowell dopping another stroke at the same hole to slip out to three over
Thompson, who had led after the first round with a tournament best 66 only to follow up with rounds of 75 and 74, set the clubhouse standard when he signed for a 67 and a two-over total of 282.
Former major winners Els, David Toms and Padraig Harrington were all still in contention at three over par level with McDowell.