Jason Day is three shots behind leader Dustin Johnson midway through the final round of the US Open as he continues to struggle with vertigo.

After starting in a tie for the lead, the Australian has dropped one shot on the front nine to be three-under par overall, three shots off the lead in a tie for fourth.

Day sits equal with compatriot Adam Scott, whose closing-round 64 was the best round of the week.

Day’s playing partner Johnson holds a two-shot lead over Masters champion Jordan Spieth (10 holes) and South African Branden Grace (10 holes).

Day is playing with his trainer and a vertigo specialist in close proximity as he continues to try to recover from Friday’s episode where he collapsed on his final hole.

Day bogeyed the fourth hole after a terrible three-putt and while he bounced back with a birdie on the fifth, back-to-back bogeys on six and seven and a birdie on eight.

Young Australian Cameron Smith is still holding his own, one-over through 11 holes in his major debut.

John Senden posted a two-under 68 to move to two-over and tied for 12th.