Phil Mickelson will go into the final round of the US Open as the only man under par as Luke Donald and Justin Rose suffered late lapses on the third day at Merion.
Mickelson recovered from an uncertain start with three birdies on the inward half, although he bogeyed the brutal final hole to return a battling 70 and post one under.
Donald, Hunter Mahan and Charl Schwartzel all got to two under for the tournament only to fall victim to the treacherous closing holes on the East Course.
Hopes of a first English champion since Tony Jacklin in 1970 were raised when Donald's sublime iron play set up birdies at the eighth and 10th.
But he failed to covert delightful approaches at 12 and 16, and he bogeyed 17 before blocking his approach into a terrible lie at the last, where he hacked over the green and ran up a double-bogey six to slip to one over.
In the group ahead, Rose atoned for mistakes at five and six with birdies at the 10th and 13th only to bogey the last two as he matched Donald's 71 to lie two adrift of Mickelson.
The English challenge suffered a further blow when Ian Poulter, who got back to one over with birdies at six and eight, pulled his drive out of bounds at the 15th and double-bogeyed before dropping further shots at 16 and 18.
After a raft of high scores early on, including a 10 for Sergio Garcia at the 15th, Schwartzel made the first significant charge as he hit back from a six at the second with four birdies over the next eight holes.
But he was another to bogey the last two holes as he slipped to even par alongside Mahan, who charged into contention with four birdies in seven holes after the turn.
Like Schwartzel, Mahan had to settle for a 69 after a bogey-bogey finish, while veteran Steve Stricker managed to close with a pair of scrambling pars to return a 70 and remain at even par.
Despite referring to himself as "Fairway Phil" at the start of the week, Mickelson hit only three of his first eight fairways and dropped out of the lead with bogeys at the third and fifth.
But he refused to panic and responded with well-crafted threes at 10 and 11, and he converted a stunning tee-shot to the 253-yard 17th before falling foul of the 18th - where there were no birdies all day.
Billy Horschel remained in touch on one over despite a scrappy 72, although he fought back well from dropping three shots on the outward half.
Jason Day is a further shot back after taking some gloss off a 68 with a closing bogey, while Rickie Fowler matched the best round of the week with a four-birdie 67 to get back to three over.
But Tiger Woods and Rory McIlroy, playing together for the third straight day, tumbled out of contention and also suffered the indignity of being outplayed by Gonzalo Fernandez-Castano.
The world's top two both birdied the first before crashing down the leaderboard - Woods dropping three shots on four holes and McIlroy leaking four in five.
McIlroy's 75 left him nine off the lead on eight over, with Woods one further adrift after his worst round as a professional in the US Open.
LEADERS: -1 Mickelson; Lev Mahan, Schwartzel, Stricker; +1 Donald, Rose, Horschel; +2 Day; +3 Fowler. (+8 McIlroy; +9 Woods).
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