A weather warning sign hangs beside the leaderboard at Merion Golf Course
Play was suspended less than two hours into the first round of the US Open due to severe weather conditions at Merion Golf Course.
Torrential rain started falling shortly before 9.15am local time and, as thunder rumbled overhead, there was soon standing water on several of the greens.
The biggest cause for concern was the 11th green, which almost flooded in last Friday's heavy rain due to the creek which runs down the left of the fairway and then curls round in front of the right-hand side of the green.
England's Ian Poulter held the lead with three birdies in three holes before play was suspended. Eleven players are under par.
Five-time US Open runner-up Phil Mickelson was also among the early starters after his cross-country trip, the left-hander having flown home to California on Monday.
Mickelson attended his daughter's eighth-grade graduation yesterday afternoon before flying back in time for his 7.11am tee time alongside Steve Stricker and Keegan Bradley.
How long play would be possible remained to be seen, with the forecast saying thunderstorms were likely and an 80 per cent chance of rain on a course already playing very soft following almost six inches of rain in the past week.