Self-possessed and unexcitable, Tennell handled the immense pressure of Olympic qualification with no outward sign of nervousness on her face or in her performances.

She landed her triple Lutz-triple toe loop combination jump here with metronomic precision. According to the skating website Ice Network, Tennell has not missed any triple jump in her last three competitions.

Image Karen Chen, the defending champion, was third on Friday night. Credit... Chang W. Lee/The New York Times

“I’ve never been a nervous competitor,” Tennell said. “I’ve always really enjoyed competing in the energy of the arena.”

A redemptive performance by Nagasu returned her to the Olympics after she was left off the team for the 2014 Winter Games in Sochi, Russia, in a controversial decision by American skating officials. She is the most mature and elegant of the American women and possesses the most difficult jump — a triple Axel, which requires a takeoff from a forward position and three and a half revolutions in the air.

Nagasu has been alternately brilliant and erratic in her career, sometimes troubled by self-doubt. But she finished fourth at the 2010 Winter Olympics in Vancouver, British Columbia. And if she can land the triple Axel in South Korea and skate consistently, she might have a chance to win a medal in a sport now dominated by Russian teenagers. No American woman has won an Olympic skating medal since Sasha Cohen took silver at the 2006 Winter Games in Turin, Italy.