LAS VEGAS—Miles Robinson scored on a header in the 117th minute, and a United States junior varsity lineup upset a mostly front-line Mexico team 1–0 on Sunday night to win the CONCACAF Gold Cup. Kellyn Acosta, one of two players in the U.S. starting lineup who gets playing time when the first-choice roster is together, took a free kick, and Robinson outjumped Edson Álvarez and headed the ball in on one hop to the right of goalkeeper Alfredo Talavera. Robinson, a 24-year-old defender in his fourth Major League Soccer season with Atlanta, got his third international goal in nine international appearances, his second goal of the tournament. Matt Turner got his fifth shutout in six matches of the Gold Cup, the championship of North and Central America and the Caribbean. The Americans won all three knockout matches by 1–0 scores. The United States won its seventh Gold Cup title, its …