Gabriela Ruffels’s exceptional composure carried her again Saturday at the U.S. Women’s Amateur: The sixth-seeded defending champion capitalized on both par-3s on the back nine to advance to Sunday’s final at Woodmont Country Club in Rockville.

The senior at Southern California with an athletic pedigree courtesy of parents Ray Ruffels and Anna-Maria Fernandez — both former professional tennis players — outlasted No. 2 seed Valery Plata, 2 and 1, clinching the semifinal on a conceded par at the 17th hole.

“Every player at this point is going to be good,” said Ruffels, 20. “I knew that coming into the match and expected it, and [Plata] played great today. It was a great match again. Nothing is easy out here, so just super happy to be able to get out there tomorrow.”

Standing in the way of Ruffels’s bid to become the first repeat champion since Danielle Kang in 2010 and 2011 is No. 16 seed Rose Zhang, a high school senior with steely resolve who reached Sunday’s 36-hole championship with a 2-and-1 victory over No. 13 Alyaa Abdulghany. Zhang, 17, went 2 up after three holes against Ruffels’s USC teammate and moved to 3 up at the turn before losing Nos. 11 and 12. A birdie at the par-4 17th ended the match as Abdulghany made a bogey on the unforgiving North Course.

“[Taking an early lead] helped out a lot because it boosted my confidence and to keep persevering through the round,” Zhang said. “It made me feel assured that I can play out here confidently and aggressively.”

After Zhang won her match with her father serving as her caddie, she waited at the 17th green to watch the win by Ruffels, whose mother, a former tennis national champion for the Trojans, walked with her group on a rare August afternoon without oppressive humidity.

Four holes earlier at the ­122-yard par-3 13th, Ruffels had a 40-footer she said after the match she was simply trying to get close. The ball instead found the bottom of the cup.

She lost the next hole and halved No. 15 before a clutch par at the 188-yard 16th, where Plata, the Big Ten player of the year with Michigan State, made a bogey.

“I never know what to think,” Ruffels said when asked to compare this week with last year’s U.S. Women’s Amateur. “This tournament is so crazy, a mix of emotions all the time, roller coaster. Just so happy right now.”

Last year, Ruffels beat Albane Valenzuela, who played at Stanford, 1 up, making birdies on four of the final five holes at Old Waverly Golf Club in West Point, Miss., to become the first Australian to win the U.S. Women’s Amateur. She beat two other Stanford players, Andrea Lee and Brooke Seay, during the event.

Zhang is a Stanford commit who grew up in Irvine, Calif., and took up golf when she became curious after one of her father’s friends dropped off a set of clubs at the house. Among the highlights of her career was making the cut at last year’s U.S. Women’s Open, finishing tied for 55th at 7-over 291 at the Country Club of Charleston in South Carolina.

“It’s honestly surreal because I actually watched her last year win this women’s amateur, and it just makes me feel so honored to play with her since she’s such an amazing player and an amazing person,” Zhang said of facing Ruffels in the championship match.

One of the most anticipated matches of the week unfolded Saturday morning in the quarterfinals: Ruffels rallied down the stretch to defeat Emilia Migliaccio, 1 up, with a birdie at the 18th.

Ruffels used an 8-iron to stick her approach at the final hole within six feet while Migliaccio was facing a 20-footer from the fringe. Migliaccio nearly drained the putt, grazing the left edge, and stood by trying to hold back tears as Ruffels stood over her ball. Ruffels remained stoic as her putt dropped into the cup.

Migliaccio had been among the favorites to win her first U.S. Women’s Amateur after she entered the week at No. 3 in the World Amateur Golf Ranking. The Wake Forest senior was the highest-ranked player in the field.

Ruffels was 2 down through eight holes, got one back at No. 9 and squared the match at No. 10, making par as Migliaccio carded a bogey at the longest hole on the course. She went down again with a bogey at the 532-yard 15th.

A birdie at the par-3 16th leveled the match, and the players halved 17, setting up the drama at the closing hole.

“I think my irons held up, and my putting at the start, it was pretty good,” Ruffels said. “Such a tough course. Overall really happy and can’t wait to get back out there tomorrow.”