American Andrew Landry set about taming the fearsome Oakmont Country Club as day one of the US Open was interrupted by weather delays.
The Pennsylvania layout is regarded as one of the most testing in North America, with Angel Cabrera winning with a five over total the last time the event was staged here in 2007.
Many had expected anything close to level par could prove to be a winning score this week but Landry set about defying all expectations as he reached five under after 13 holes to open up a a three-shot lead.
Lee Westwood was in the group three shots back alongside Americans Bubba Watson and Bryson DeChambeau, and New Zealander Danny Lee when play was halted for a second time at 12.07pm local time.
World Number 624 Landry had birdied the tenth, 17th and second when play was first stopped at 10.04am and, after a delay of one hour and 19 minutes, he returned to make gains on the third and fourth to pull away from the field.
Westwood made a birdie on the 12th and then dropped a shot on the 13th before bouncing back in brilliant style, holing out from 124 yards on the next for an eagle.
He then parred his way to the turn either side of the first delay, missing a good chance for a birdie as he three-putted after driving the 17th.
Two-time Masters Tournament winner Watson had an up-and-down day with four birdies and three bogeys on the front nine before he rolled in a 49-footer on the tenth to get to two under.
DeChambeau was level par at the time of the first delay but returned to chip to within two feet for a birdie on the 14th and followed that with a 48-foot putt on the next to also join the group in second.
Lee had birdies on the fourth and sixth in his eight holes.
Matthew Fitzpatrick was in the group at one under after a dramatic first eight holes where he holed a bunker shot on the second and rolled in from 41 feet on the sixth before dropping a shot on the next.
Frenchman Romain Wattel had two birdies and a bogey in his first 11 holes to sit alongside Fitzpatrick and Americans Zach Johnson, Harris English and Kevin Streelman.
Ireland's Shane Lowry - who pitched in on the first - France's Grégory Bourdy, 2014 winner Martin Kaymer and defending champion Jordan Spieth were then part of an 11-man group at level par.
Rory McIlroy, Danny Willett, Russell Knox, Rafa Cabrera Bello and Soren Hansen were then all two further shots back.