CONWY, Wales—Top-ranked amateur Rose Zhang capped off an unbeaten week as the Americans won six of the eight singles matches Saturday to beat Great Britain and Ireland in the Curtis Cup. Zhang went 4–0–1 for the week at Conwy Golf Club, finishing with a 1-up victory over Emily Toy in the anchor match. By then, the United States had won so many matches that the Curtis Cup had already been clinched. That added to a 12 1/2–7 1/2 victory for the United States, which extended its dominance in the premier team event for women’s amateur golf. Since the Curtis Cup began in 1932, the Americans now lead the series 30–8–3. The score was tied at 6 going into singles. As the defending champion, the Americans only needed to win four points from singles to retain the cup. “But that wasn’t our goal,” Rachel Kuehn said after her 2-up victory over …