Great Britain and Ireland will need to come from a point down on the final day to end their wait for a Walker Cup success.
Having taken the morning foursomes session 3-1 at Cypress Point, California, the visitors struggled in the afternoon singles as the USA took a 6.5-5.5 overnight lead.
Eliot Baker almost produced an unlikely par on the 18th to send the match into the second day level, but after missing the fairway and hitting a tree by the green, his putt remained on the edge of the cup.
Jase Summy, who had fallen behind after twice putting off the 14th green, made no mistake to claim the match and give the US the lead.
Great Britain and Ireland have not won the trophy since 2015 and have not triumphed away from home since 2001.
Their pursuit of the elusive victory made a great start, Baker and Stuart Grehan combining to beat Ethan Fang and Preston Stout by a single hole as the visitors won the opening three matches of the morning foursomes.
Connor Graham and Tyler Weaver beat Jackson Koivun and Tommy Morrison 3&1 with Charlie Forster and Luke Poulter – son of European Ryder Cup star Ian – seeing off Stewart Hagestad and Ben James 3&2.
Michael La Sasso and Summy avoided the whitewash in the final match with a 4&2 win over Cameron Adam and the US maintained their momentum early in the singles.
Graham beat world number two amateur James 3&2, but the US claimed four wins before Niall Shiels Donegan stemmed the flow as he beat Jacob Modleski on the last.
Grehan missed a birdie putt on the last he tied with Fang before Summy’s late point edged the hosts in front.