The Scunthorpe-born golfer was faced with a Hazeltine course deemed as "difficult" by Jack Nicklaus and at 7, 151 yards also carried the tag of being the second longest in Open history.
Ramsay, 23, who played alongside Mickelson in the Masters in April, became the first British US Amateur champion in 95 years when he beat American John Kelly at Hazeltine National in August 2006.