Brooks Koepka and Henrik Stenson took advantage of Dustin Johnson's woes to take a share of the U.S. Open lead and Phil Mickelson was penalised for hitting a moving ball on a dramatic moving day.
Johnson teed off with a four-shot lead on Saturday, but the 2016 champion had a nightmare on the front nine in demanding conditions at Shinnecock Hills.
The world number one double-bogeyed the second and dropped another four shots before the turn to slip back to two over before making a first birdie at the 11th in Long Island, where lightning quick greens and pin placements were causing all sorts of problems.
Koepka and Stenson had leapfrogged Johnson to lead him by a solitary stroke.
As much of the field struggled in such tough conditions, Koepka and Stenson were level par through 12 and 11 holes respectively.
Stenson came up with his first birdie of the day at 10 to join the defending champion, who started with a bogey before hitting back with a gain at the second and also dropped a shot at the 12th immediately after a second bogey.
Tony Finau and Daniel Berger matched the best round of the week with four-under 66s, putting themselves firmly in contention along with Justin Rose - who was level with the American duo on three over with five holes to play.
Mickelson caused huge controversy when he was given a two-shot penalty after chasing his putt and hitting his ball back towards the hole as it continued to roll down the slope on the 13th.
That turned an eight into a 10 and the five-time champion was way back on 17 over after signing for an 11-over 81 on his 48th birthday.