BY MELISSA RUGGIERI

For fans of Chris Brown and Trey Songz, the doubleheader “Between the Sheets” tour would have been heart-skittering enough.

But then throw in surprise appearances from R. Kelly, B.o.B., Keith Sweat, T.I., Future and Migos, among other rap and R&B luminaries, and suddenly you had a show to rival Usher's star-studded homecoming in December.

The shriek-o-meter at Philips Arena Monday night was already threatening to burst by the time Songz, the bigger Romeo of these Virginia natives, took the stage after a fake coin toss between the tour mates on video (as if Brown would be anything less than a headliner?).

Rising from under the stage in a plume of smoke, Songz flashed his million-dollar smile and, as six scantily clad female dancers writhed, bore into “Foreign.”

Considering the name of the tour, pretty much everything about the show centered on sex (feisty opener Tyga was a tad more explicit on club bangers “Make it Nasty” and “Main Chick” – yet women appeared thrilled to sing along to the brashly misogynistic lyrics).

Trey Songz showcased his versatile voice. Photo: Robb D. Cohen/RobbsPhotos.com.

Credit: Melissa Ruggieri

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Credit: Melissa Ruggieri

Songz, at least, drizzles romance atop his bedroom teases. His “Cake” is an Usher-lite head-nodder, while “All We Do” gushed with emotion thanks to Songz’s versatile voice.

With no band in sight for either Songz or Brown (though the latter had a couple of male backup vocals providing an assist), the musical backing was left to tracks. No one in the audience seemed to care.

The sold-out throng escalated their shrieking when deep bass thrusts announced the first guest –  Atlanta’s B.o.B. – who popped out to add his nimble wordplay to “Not for Long” with Songz.

The 30-year-old loverman is primarily a singer, not an entertainer, but he ably worked the stage in his black V-neck T-shirt, a wad of gold chains hanging from his neck.

It seemed that most in the predominantly female crowd were happiest when a video of Songz stripping down to his six-pack played as a prelude to “I Invented Sex.”

But as the light stayed down, indicating that Brown would soon slowly emerge from a space in the stage wall, baseball cap tugged over his bowed head and plum-colored hair, the frenzy escalated.

Backed by a team of male dancers, Brown launched his portion of the show with “X,” winding up his body as the song reached its EDM-like climax and then bursting into one of his fleet-footed moves.

Brown’s voice, a more nasal counterpoint to Songz’s creamy croon, wasn’t the focus of “Came To Do.” Far more interesting was his controlled, loose-limbed flailing; at times it looked as if his shoulders might wiggle away unattached from his body.

No doubt, despite his unarguable talent, Brown is still a polarizing figure. His frequent run-ins with the law and his own misguided decisions have continuously derailed his still-escalating career (the Atlanta show was originally slated for last month, but was postponed because Brown hadn't completed his court-ordered community service).

But when he requested, of course, that “all my ladies make some noise,” the ensuing roar sounded an awful lot like forgiveness.

Brown looked even happier when R. Kelly and Keith Sweat showed up. Photo: Robb D. Cohen/RobbsPhotos.com.

Credit: Melissa Ruggieri

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Credit: Melissa Ruggieri

Brown utilized his stage time to travel back to those more innocent days, employing lasers to accompany “Wall to Wall” and his original Gumby-like moves on his 2005 breakthrough, “Run It.”

Despite the overuse of tracks, Brown was singing on the majority of his songs, even reminding of his young Michael Jackson vocal tendencies on the silken-grooved "Strip" and, obviously, the "Human Nature"-sampling "She Ain't You."

By the time both Songz and Brown finished their respective sets, it likely would have been enough to sate most fans. But it turned out that was merely the warm up.

The pair re-emerged together, slapping hands at center stage before retreating to red chair erected on opposite ends of the stage.

They took turns unspooling their most emotive ballads – first Brown, now wearing a fur-collared jacket, with the steamy “Take You Down,” then a red hoodie-clad Songz with “Neighbors Know My Name.”

Given the similar pace of all of the songs (“Love Faces,” “Don’t Judge Me,” etc.), the segment started to drag until Songz and Brown crisscrossed the stage for their homage to R. Kelly, “Songs on 12 Play.”

And then…Kelly himself strolled onto the stage, stogie in hand, to perform a medley of his hits, including “Ignition” and “Bump N’ Grind.”

Brown and Songz continued the surprise-a-thon with Sweat, whose nearly-20 year-old “Nobody” still resonated – and was heartily sung by thousands of fans who weren’t even born when it was released.

The stars of the show, meanwhile, sat respectfully to the side and sang backup as Sweat worked the stage.

The encore of this three-hour-plus night kicked off with more dry ice, Songz in a white and black sleeveless ensemble and the jacked-up crowd singing along heartily to “Heart Attack.” Little did they know the parade of stars still to appear (T.I., Future, Yo Gotti, Young Jeezy and Migos among them).

For fans, the Atlanta stop of “Between the Sheets” could breathlessly be described as ...epic.

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