The final round of the US Open got off to an extraordinary start after a wayward shot from British hopeful Luke Donald struck a volunteer.
Donald needed a driver to try to reach the par-three third and hooked it well left of the green, where it struck a young woman apparently walking with the group ahead.
She needed medical attention before eventually being helped to her feet by two police officers, with a visibly shaken Donald ensuring she was okay before playing his second shot onto the green and two-putting for bogey.
Playing partner Justin Rose also dropped a shot on the same hole to fall three behind, while Rory McIlroy's frustrations at taking a quadruple-bogey eight on the 11th boiled over when he leant on one of his clubs so hard that he bent the shaft.
Donald and Rose are aiming to claim their first major titles and end a 43-year wait for an English winner of the US Open.
American Shawn Stefani had carded the first ace in a US Open at Merion thanks to a lucky bounce on his four-iron tee shot to the 229-yard 17th.
Steve Stricker, one shot off the lead held by Ryder Cup team-mate Phil Mickelson starting the day, hit his tee shot out of bounds on the par-five second and, after finding the fairway with his second ball, shanked that out of bounds as well.
The resulting triple-bogey eight dropped Stricker four behind Mickelson and South African Charl Schwartzel, the former Masters champion having birdied the first.