'Dancing With the Stars' 2015: Nastia Liukin and Derek Hough Cut in Season 20 Semifinals

— -- After finishing the first night of the semifinals with a perfect score and tied for first place, Olympian Nastia Liukin and five-time mirror ball champion Derek Hough were voted off "Dancing With the Stars" Tuesday night, just one week shy of the season 20 finale.

Liukin, 25, has performed well during the nine weeks of competition, consistently earning judges' scores that have placed her at or near the top of the leaderboard.

Despite her top scores, however, she said she’s “not really” surprised by her elimination.

“First of all, being able to dance with Derek one last time really meant so much to me, and that dance was kind of the perfect way to go out,” Liukin explained on “Good Morning America” today, referring to the Viennese Waltz coached by head judge Len Goodman. “It was such a special moment not only to share that with Derek but then with Len, and really tell his story of his career. It really was a special dance. I definitely didn’t want to leave, but it was a good night.”

She has danced some routines with pro dancer Sasha Farber since Hough sustained an injury going into the seventh week of the season, and was tied for first place on the leaderboard Monday after earning perfect scores from the judges for her quickstep with Farber and her Viennese Waltz with Hough.

“It’s been a fantastic season and an ironic one, too,” Hough said. “Having her dance with two partners and handling that so flawlessly and effortlessly, it was incredible.”

Elimination in the competition is based on a combination of judges' scores and viewer votes.

This is the ninth week of the season. Actress Rumer Willis, Army veteran Noah Galloway, and R5 band member Riker Lynch will advance to the finals on Monday.

As for who Liukin thinks will take home the mirror ball trophy, “It’s so hard to say,” she said. “Every single couple has a different strength and that’s what’s so amazing to see.”

Galloway, a double amputee who has impressed judges and fans with his determination, finished fourth on the leaderboard last night. Willis -- a favorite of judges and fans and who is especially adept at the classic ballroom styles of dance -- was third. Lynch, who has impressed judges with his flair and technical ability, was tied with Liukin for first place.

Tuesday’s show featured performances from the cast of "Teen Beach 2" and rapper Flo Rida.