In the United States' first four games of the 2015 FIFA Women's World Cup, O'Hara did not see any playing time. O'Hara made her first start of the tournament in the quarter-final game against China PR. She was replaced by Christen Press in the 61st minute. O'Hara scored her first career international goal in the United States' 2–0 victory over Germany in the semi-final. In the final against Japan, O'Hara entered the game in the 61st minute to replace Megan Rapinoe. The United States went on to defeat Japan 5–2, winning the first World Cup title since 1999 and the third overall World Cup title for the United States since the inaugural Women's World Cup in 1991.