But, PEOPLE has learned, the two actually crossed paths during rehearsal. Timberlake was first, and then Spears came on stage to run through her part. "They said 'hi' to each other. Justin was very cool," a source says.
Spears also lingered and watched Timberlake's entire sound check from the first few rows of the stands.
Adds another source, "This was a night for [Britney] to enjoy, and not stress over. This was a good moment for her to just enjoy and have fun."
And enjoy she did. Dressed in satin black pants and white suit shirt with ruffle, Spears has been appearing in a taped segment during Madonna's "Human Nature" performance since the beginning of the tour. Her "It's Britney, b----!" segment she did live.
Kisses Hand This TimeMadonna greeted her with "Hi Britney!" And Spears, with her blonde hair flowing and red lips smiling, moved to the beat as she sang the last chorus on "Human Nature" with Madonna.
"She's not your b----" Madonna proclaimed, pointing at Spears who replied with her classic line: "It's Britney, b----!"
Madonna had to swing her around three times to get her to loosen up a little bit and, in a far cry from the 2003 smooch, kisses Spears on the hand as her platform sunk below the stage.
"4 Minutes" came on and remixed into "Vogue" as Spears disappeared from view.
Timberlake later joined Madonna to belt out a full rendition of their duet "4 Minutes." Dressed in black pants, a black jacket and scarf he and Madonna really went at it, playing off two dancers, dancing and grinding on each other. The crowd loved it.
"It was great!" a fan told PEOPLE at the show. "They really kept each other going up there. And, wow, only Madonna could bring the two exes together!"
Salute to ObamaAt the close of the concert, a photo of President-elect Barack Obama flashed on the screens as Madonna announced, "We have something to celebrate! I'm the happiest girl on the planet right now."
She continued: "Sorry to hear we didn't win on Prop 8, but don't give up the fight. If we can have an African American in the White House then when we can have gay marriages."
Madonna, who split from director Guy Ritchie last month, will wrap up the North American leg of her tour Nov. 30 in Mexico City.
Reporting by MARY MARGARET and BETH PERRY
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1985: Madonna embarks on her FIRST tour!
2003: Post-Brit breakup, JT moves on with Cameron Diaz