By People Staff
Updated May 20, 2008 12:00 AM

Usher‘s pre-taped, edited performance for tonight’s Dancing with the Stars finale may look seamless, but what happened behind the scenes at the singer’s May 13 taping left host Tom Bergeron and company scratching their heads–and scrambling to set up for the live show.

First, the 29-year-old singer arrived late, throwing the entire production behind schedule. Then, while appearing to lip-synch two songs–”Yeah!” and “Love in This Club”–he fell out of step with his choreography, turning the wrong way once and losing his mic a second time. With each mistake he walked offstage.

The performance then went further off-course when the singer took a long break to get a drink. “He was ridiculous,” a source tells PEOPLE. “Such a diva.” Following Usher’s act, the DWTS cast and crew had only 15 minutes to prepare for the live show (rather than the standard 45-minute post-taping buffer.) “The dancers were all at their trailers ten minutes before the show was supposed to go live, like, ‘Don’t we have a live show to do?” a source says. “There was a lot of holdup. We almost didn’t make it.”

The judges–who were dressed in their finale show formalwear for the pre-show taping–made a quick costume change, while a team of grips frantically wiped away scuff marks on the dance floor left behind by Usher and his dancers.

And just in the nick of time: the live show went off without a hitch. “It’s never gotten that close before–that was scary,” Bergeron told PEOPLE about the taping frenzy. Joked the good-natured host: “I don’t even know that judges Len and Bruno put on pants to come back, they changed outfits so fast!”

Usher’s rep did not return phone calls, while Dancing‘s reps declined to comment.

The second part of the DWTS finale airs tonight on ABC (9 p.m., EST). Mark Allan/WireImage