Americans battle for lead as Day recovers from collapse

US Open contender Jason Day's continuing participation in the championship was in doubt on Friday night after the Australian collapsed on the course near the end of his second round.

Day, whose season has been affected by still unexplained dizzy spells despite brain scans, blood analysis and sleep tests, had been two shots off the then-lead of five under par as he walked towards his ball in a bunker at the ninth green, his final hole of the day.