Michael Becker / Fox

If you watched Caleb Johnson and Jena Irene battle it out on American Idol's top 2 performance show Tuesday night, you saw an epic showdown. What was happening off-camera at Los Angeles' Nokia Theatre? Read on for 9 things you didn't see on TV.

1. In a venue that holds 7,000 people, there were only three Idol finalists from past seasons (though many more are expected at Wednesday's finale). Season eight's Scott MacIntyre and his wife Christina flew in from Nashville to attend and were seated in the front row. Seated further back were Erika Van Pelt and Jeremy Rosado from season 11.

2. The number of Idols goes up if you count the current crop of finalists. The season 13 eliminated contestants from the top 13 were seated together in the second row, right across the aisle from the MacIntyres. That required a whole lot of seat fillers to come running when this year's Idols were called to the stage to join Johnson and Irene in singing Kelly Clarkson’s “Breakaway.”

3. One new thing we learned on Tuesday night: old Idol sets aren't discarded, they’re stored. Returning to the stage were the gyroscope-looking towers with the revolving American Idol logos. They haven't been seen on the CBS stages for at least a couple of years. For the performance finale, the oval Idol logos weren't spinning around, they were stationary.

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4. Keith Urban and Jennifer Lopez have doled out their share of standing ovations during the season. They gave another one Tuesday night to Johnson when he sang "Dream On," the Aerosmith song chosen for him by Idol creator and executive producer Simon Fuller. The two judges didn’t wait for the end of the song, they were on their feet about three-quarters through. Harry Connick Jr. remained seated.

5. A new addition to the American Idol set on stage 36 at CBS this season was a collection of large, lighted photos of the top 13. As contestants were eliminated, their photos were dimmed. Only two photos had to be transported to the Nokia, and they were hung high above the stage. Johnson and Irene were thus smiling down on everyone.

6. The Idol finale was a hot ticket but just a few minutes before the live broadcast was about to begin, there were hundreds of empty seats. Ticketholders had been asked to be seated by 4:30 p.m., so they were either late, or an extraordinary number of seat-fillers were pressed into service.

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7. Just before round three of the competition was to begin, director Louis J. Horvitz gave an audio shout-out to the audience, praising them for being so great. It sounds like something you'd expect a director to say to every audience, but this was rare praise, so we suspect Horvitz really meant it.

8. When the one-hour show was over, it wasn't over. The audience was asked to stay, both by Horvitz and warm-up maestro Cory Almeida. The reason? Two numbers for Wednesday night's show were going to be pre-taped -- one by the three judges and Randy Jackson, the other by Lopez in a solo turn. A majority of audience members did stay, despite a 40-minute wait for the judges' performance.

9. Following the first take of the judges and Jackson singing a medley of Cyndi Lauper's "True Colors" and Fleetwood Mac's "Go Your Own Way" came the clue that there would be a second take as a large entourage suddenly made its way to the stage. While hairdressers and make-up artists did their thing, Horvitz announced on the p.a. that there would be another take. That second run-through was interrupted and the talent started over, so the total number of performances was 2.5.

Twitter: @Idol_Worship