Australian Adam Scott is in danger of missing the cut at the US Open after finishing at seven over on Friday, with the second round suspended due to darkness. Billy Horschel and Phil Mickelson share a one-shot lead at the top of the leaderboard at the Merion Golf Club in Pennsylvania, where soft conditions made scoring difficult. Scott, who was at three under through 11 holes and tied for second a shot back overnight, completed a 72 in his first round. But a run of four straight bogeys from the third hole was costly in his second round as he slumped to seven over, with the projected cut eight over. John Senden is the best-placed Australian at one over, while Mathew Goggin is a further shot back after he followed up his 68 with a four-over 74. Jason Day (three over through 14) and Geoff Ogilvy (four over) should make the cut. Alistair Presnell and Aaron Baddeley (both eight over) could play a part on the weekend, while Marcus Fraser (12 over) and Marc Leishman (13 over) are set to miss out. Mickelson, who produced a round of 67 on Thursday, holed his only birdie of the second round on the 18th hole to move into a share of the lead. A group of five players including Englishmen Luke Donald, Justin Rose and Ian Poulter, American Steve Stricker and Taiwan&aposs Cheng-Tsung Pan are locked in a tie for third at even par. Poulter and amateur Pan are yet to complete their rounds after getting through 14 and nine holes respectively. It was Horschel who enjoyed a fine day to move into contention. The American started the round at two over, but a birdie at the second put him in position to make a charge, and he continued to play a mistake-free round, taking the turn at one under for the day. His surge up the leaderboard came shortly after with a birdie at the 10th and an excellent putt at the 11th also gaining him a shot to move him to three under for the round. A dropped shot at the 13th slowed his progress before he regained that shot with a birdie at the 18th. Mickelson holed three bogeys before finally getting the birdie he needed to move into a share of the lead after the siren. The world&aposs top two Tiger Woods and Rory McIlroy remain in contention at three over after producing even-par rounds of 70. Several big names including Scott are in danger of missing the cut as the field struggles with the challenging conditions and course. Martin Kaymer is a shot behind Scott after a triple bogey at the fifth ruined his second round. Graeme McDowell, the 2010 US Open champion, is a near certainty to miss out on the final rounds after a 77 left him at 13 over. Webb Simpson and Sergio Garcia (both six over) and Lee Westwood and Bubba Watson (both seven over) are also well back. Garcia is one of over 60 players yet to finish their rounds.