The disruption had been widely expected for the last few days with a strong storm system tracking out of the Midwest and into Pennsylvania and there were fears that worse was to come during the day.
When play was suspended, English Ryder Cup hero Ian Poulter had stormed to the top of the nascent leaderboard with birdies at his first three holes.
Big-hitting Belgian Nicolas Colsaerts, a teammate of Poulter at Medinah last September, was at two-under after seven holes.
He was joined on that mark after just a handful of holes by South African pair Tim Clark and Charl Schwartzel along with American Charley Hoffman.
"This is one really nasty looking storm that will hit at 9am and last the entire day. Not much golf," Poulter had posted on his Twitter account before his round got going.
Tournament favorite Tiger Woods one was not due off until 19:14 (SA time), going out with the two players next to him in the global rankings - Rory McIlroy and Adam Scott.
But the entire 156-strong field were subject to what the weather gods were about to throw at them.
The historic East course at Merion has already been doused by heavy rain in the last few days and there was apprehension over what might follow on Thursday with the possibility of damaging winds, flash flooding and hail.
United States Golf Association (USGA) executive director Mike Davis believes that Merion, at 6 996 yards, the first US Open course under 7 000 yards since Shinnecock Hills on Long Island in 2004, will survive both the storm and an assault from the world's best golfers.
"There's a wonderful balance to the course in terms of ebb and flow," he said.
"There are opportunities to catch up with birdies, but there's also holes that are as hard as any that you'll see in any US Open. It really is magical."
Among scheduled early starters were last year's Masters winner Bubba Watson, five-time runner-up Phil Mickelson, in-form Matt Kuchar and English challengers Luke Donald, Lee Westwood and Justin Rose.
Woods, whose last major win came at the US Open at Torrey Pines in 2008 when he won an 18-hole playoff against Rocco Mediate on what turned out to be a broken leg, is back near his best with four tournament wins this year already.
But to seal his comeback he needs to win a 15th major title and move to within three of the all-time record of 18 set by Jack Nicklaus when he won the 1986 Masters.
Woods, at 37, nine years younger than Nicklaus was when he last won at Augusta National, says he is prepared to take on the playing conditions no matter what they are - wet and soft or dry and hard.
"I've played Opens under both conditions where its dry and soft. I've won on both conditions, which is nice," he said.
"At Torrey (Pines) it was dry. Pebble (Beach) was dry. And Bethpage was soft and slow."
Playing partner McIlroy is still wating for his 2013 season to catch fire after an equipment change that has proved more problematic than he expected.
But he has a record of rebounding from poor form at US Open time and has sought inspiration in Philadelphia by visiting "The Rocky Steps" made famous by Sylvester Stallone in his film portrayal of boxer Rocky Balboa.
The field includes 10 former US Open winners and a host of major champions from six continents.