Fox fired an opening round 3-over-par 73, which had him tied for 108th.
Starting on the 10th hole at Pinehurst, Fox birdied the 11th before a bogey at the 13th and a double bogey at the 14th.
He played par golf until the second with another bogey, a birdie at the fifth and then a bogey at the seventh.
Fox, who moved to the US PGA Tour from Europe last year, is playing the US Open for the fifth time.
He missed the cut in his first three outings and finished tied for 43rd last year.
Pinehurst is where New Zealander Michael Campbell won the US Open in 2005.