A strong performance from American outsider Billy Horschel has seen the 26-year-old finish day two as joint-leader of a congested field at the US Open, alongside experienced compatriot Phil Mickelson.

Horschel set a record during his three-under-par round of 67 at the Merion Golf Club today, hitting all 18 greens in regulation.

His second-round score of 67 means that Horschel is one of only two players under par in the tournament, with a whole host of familiar names including Luke Donald one shot further back.

Mickelson managed to take a share of the lead with his final shot of the day, sinking a lengthy putt for birdie on the 18th green to join Horschel on one-under par.

Donald is also firmly in contention after finishing a strong second round early on another hectic day at the Merion, carding a fine round of 72 to stay firmly in contention.

Early in the session Donald took a clear lead, but bogeys in successive par fives saw the Englishman slip back into a crowded pack chasing the leaders.

British interest in the event remains high, with Ian Poulter and Justin Rose also just one shot behind the lead alongside Steve Stricker.

Star names Tiger Woods and Rory McIlroy are both four shots back at the halfway stage, after the pair hit identical level-par rounds of 70 earlier this evening.

Play was suspended for the day at around 1.45am UK time due to bad light, with more than 30 players still to complete their seconds rounds.