Forgive U.S. defender Julie Johnston if she takes a moment this weekend to consider how dramatically her life has changed in the past seven months.

With the Women’s World Cup knockout stage starting Saturday, Johnston is the breakout star of a U.S. defense that has become the strongest component of a team usually known for its attacking firepower. She was a long shot to make the World Cup roster. She had done little to impress in three sub appearances last year. Coach Jill Ellis, who was still searching for answers for a shaky back line, told Johnston she might get dropped.

Then came a chance conversation with veteran midfielder Carli Lloyd when Johnston mentioned she was heading to Philadelphia to see her boyfriend, Eagles tight end Zach Ertz. Lloyd, a massive Eagles fan, suggested they work out together with Lloyd’s trainer James Galanis, an Australian known for his emphasis on footwork, touch and fundamentals.

For Johnston, 23, it was like being asked to sit at the cool table in the middle-school cafeteria. “That was a huge turning point for me,” Johnston, who spent hours with Lloyd doing drills she hadn’t done since youth soccer, said in a recent interview.

With longtime central defender Christie Rampone nursing back and knee injuries, Ellis gave Johnston another shot, pairing her with Becky Sauerbrunn for what has largely become an unyielding wall in the U.S. back line. Through three games, including two against top-10 teams and a third against African champion Nigeria, the U.S. gave up just 2.7 shots on goal a match and conceded just a single goal—even though Johnston, known as one of the team’s best players in the air, often ends up stalking the opponent’s goal.