‘Dancing With the Stars’ 2015: Bindi Irwin, Carlos PenaVega Lead Final Four After Season 21 Semifinals

— -- The final four contestants on "Dancing With the Stars" each pulled out all the stops for tonight's season 21 semifinals, and with three routines, the pressure was on to perform well enough to make it to next week’s finale.

They all did.

This was the first time in the program's history that contestants had to dance three routines in the semifinals. Conservationist Bindi Irwin, Big Time Rush singer Carlos PenaVega, Army National Guardsman Alek Skarlatos and Backstreet Boys member Nick Carter and their pro partners each had to do a dance that included another dance pro, a routine to a style of dance that the couple had never before performed on the show and a dance-off challenge against a competitor, with the winner earning 3 bonus points from the judges.

Five stars were to have competed in tonight's show after actress Alexa PenaVega's elimination last week, but that number was whittled down to four when singer/TV host Tamar Braxton dropped out of the competition after finding out that she had blood clots in her lungs.

Her pro partner, Valentin Chmerkovskiy, publicly thanked her supporters during tonight's show.

"On behalf of both of us she loved every moment of it and I wish she were here to say her thank yous but on behalf of both of us it was an incredible season for me," he said. "I’m very blessed to have met Tamar and she's incredible. I wish her all the best."

Based on their judges' scores and viewer votes, Irwin and Carter had been in jeopardy of elimination tonight, however, because Braxton dropped out of the competition, no one was eliminated at the end of the show.

At the end of the night's three rounds, PenaVega and Irwin were tied for the top spot, followed by Skarlatos, and then Carter at the bottom of the leaderboard.

Tonight's top scorers: Bindi Irwin and Carlos PenaVega were tied for first place with 60 points each after their respective three routines. PenaVega earned his high score of the night for his bubbly Charleston trio, while Irwin got a perfect score for her jazz trio routine.

Tonight's standout moment: Bindi Irwin's innovative jazz trio with pro partner Derek Hough and Mark Ballas brought the audience to its feet, and the judges shared the sentiment. Bruno Tonioli called the routine "a totally compelling and intriguing work of genius," while Julianne Hough (Derek Hough's sister) praised the attention to detail in the Irwin's movements. Carrie Ann Inaba expressed her approval with several siren-like noises, explaining: "That is what I felt like watching that ... this was not 'Dancing With the Stars.' That was like a professional contemporary dance company." Irwin earned a perfect score for the routine.

Tonight’s Scores (First dance; dance-off; third dance. Total.)

Bindi Irwin and Derek Hough: 27; 3; 30. Total: 60

Carlos PenaVega and Witney Carson: 28; 3; 29. Total: 60

Alek Skarlatos and Lindsay Arnold: 30; 0; 27. Total: 57

Nick Carter and Sharna Burgess: 24; 0; 30. Total: 54