under par

The 28-year-old world number 22 carded three birdies and two bogeys in his one-under 69 as he maintained his overnight lead and moved to four under par.

Alongside Spaun at three under par, 2013 Masters champion Adam Scott made a decisive move on the back nine to stake his claim for a second major title at 44 years old.

Only three players out of a field of 156 are under par at the halfway stage with Burns making six birdies and just one bogey in a morning round that looked better as the day progressed.

Rory McIlroy found Oakmont Country Club a bruising challenge as only five players from round one's morning wave ended under par at the US Open.

Then came birdies on No. 10 and No. 11 to go to six under par.