The day started early, with the likes of Rory McIlroy and Tiger Woods having to come back and finish off their first rounds before quickly heading out for their second bash at the Merion challenge.
The course was softened up by all the rain but any talk of a low score have fallen by the wayside by now and Billy Horschel's three-under 67 was the stand-out.
Still, there are 68 players still to complete their second round, including Ian Poulter who is just one shot off the pace.
The five-time runner-up endured a tough day, especially on the greens, but managed to birdie his final hole just before the end of play to grab a share of the lead.
The Masters champion was left sweating it out to see if he would make the cut after finishing seven-over after two rounds. The cut looks like being at eight-over so he could just sneak in.
The American enjoyed a superb day at Merion as he defied the conditions to hit a superb round of 67 and grab a share of the lead with Mickelson.
The world No 1 played down injury fears and insists that he still fancies his chances of ending his five-year wait for a major title as he sits just four shots back.
The Englishman looks like finally launching a serious challenge for the US Open after he finished his two rounds in level par and just a shot off the leaders.
2003 champion Furyk was decently fancied by some this week, but he is out after coming back at +16 - although he still loved playing at Merion.
The 2011 champion ended his first round badly but battled his way to a level-par second round to match Woods' score of three-over and book a third round with his mate.