Retirement? Heck no. Prison time? Please. Feud? Uh, maybe. In a 21/2-hour main event at MCI Center on Thursday, rapper Jay-Z cooled his threats of quitting the game and delivered a knockout performance, and R&B star R. Kelly unleashed enough provocative punches to suggest he's not too worried about his legal troubles.

And when the newsmaking artists did occasionally perform side by side, the palpable tension between them (oh, the rumors are swirling, folks) was enough to make up for their sloppy teamwork.

How ballyhooed was this heavyweight bout? That Bad Boy himself, Sean "P. Diddy" Combs, was in the house, leading his serpentine entourage through the near-capacity crowd not once but twice. And who can blame the Puffy One for wanting a ringside seat?

The story line is captivating: Chicago native Kelly is facing felony child-pornography charges as a result of a videotape secured by police that allegedly shows the singer having sex with a minor. That tape was discovered in 2002 -- about a week before a collaboration between Kelly and Jay-Z, the album "The Best of Both Worlds," was released. The Brooklyn-born Jay-Z, whose relationship with bombshell Beyonce Knowles has given the former thug a mainstream sheen, immediately distanced himself from Kelly. The album landed with a thud -- and a feud was on.

But since then, Kelly, who recently released the double-disc hit "Happy People/U Saved Me," has seen his popularity grow even larger. Jay-Z delayed the retirement he repeatedly promised on 2003's "The Black Album" so the duo could record a second album, "The Best of Both Worlds: Unfinished Business" (due Oct. 26).

So everything's hunky-dory now, right? Ha! Although this tour is relatively still in its infancy, trouble's already a-brewin'. Show starts have been delayed by as much as two hours. And a stop in Cincinnati was recently canceled on the day of the show, the buzz being that Jay-Z and Kelly just couldn't get along.

When the lights dimmed not long after the scheduled starting time at MCI, a "news report" flickered to life on the 10 giant video screens framing the two-tiered stage: Two sleek black tour buses -- one with Illinois plates, the other with New York tags -- were shown barreling down a highway. A phalanx of cop cars chased the buses, and a pretty reporter screamed that SOMETHING WAS HORRIBLY WRONG! And before you could say, "O.J., anyone?" the actual fronts of two buses crashed through a faux-stone wall on the stage.

Cool effect, guys. Now, let's get ready to rumble.

Stepping off their buses in white suits and gold chains, the two busted into their 2002 duets "The Best of Both Worlds" and "Take You Home With Me A.K.A. Body," Kelly cooing the hook and Jay-Z machine-gunning his trademark rhymes. Did they acknowledge each other? Did they hug? Good lord, did they at least tip their equally bright white hats? No, no, no.

Kelly soon strutted backstage and Jay-Z took over, setting the game of "top that, buddy" in motion. Jay-Z did 20 minutes of hits (including "Excuse Me Miss," "Izzo (H.O.V.A.)," "Hard Knock Life (Ghetto Anthem)"), then Kelly did 20 minutes ("Ignition," "Thoia Thoing," "I Wish"), and on and on for five sets apiece, with nary a moment for breath-catching in between. These guys might not be chums, but their desire to steal the spotlight from each other kept the show at a whiplash pace.

Of course, there was a clear winner in this face-off. Jay-Z remains the most inventive and dexterous rapper of all time, unspooling his assault of syllable-stretching rhymes over yummy hooks and defibrillating beats. Yeah, he's a braggart, but he's just so different about it. As he shook the foundation of the downtown arena with the thunderous "99 Problems," the doomy "U Don't Know," and a cruel tease of Beyonce's "Crazy in Love" (sorry, kids: no B sightings), the video screens behind him flashed an array of images, including Huey helicopters, Kurt Cobain destroying a guitar and R.I.P. shots of Biggie Smalls, the only MC who could give Jay-Z a run for his money. He didn't make a peep about retiring -- maybe (one hopes) because he's having second thoughts.

Kelly used the video screens for different purposes: to show close-ups of his sweat-soaked abs, his pretty-boy face, his fanny -- and then back to his abs again. Kelly proved that he can be a great songwriter (the silky, smutty "Down Low"), and his falsetto sure buckled lots of bare knees. "Y'all make me feel like I'm in my living room. And when I'm in my living room, I do what I want in my living room," he spoke-sang at one point, apparently not too worried about further damaging his rep. But all too often, the smooth crooner stopped his tunes before they even got going, instead relying on pyrotechnics to get the crowd cheering. His refusal to finish much of anything grew tedious -- but not nearly as tedious as a supposedly on-the-spot improvisation about "sex in the kitchen," which he happened to improvise last year at MCI.

For the finale, Kelly and Jay-Z, both dressed in camouflage, stumbled together through a go-nowhere new song, "Big Chips," and then offered up a lackluster "Fiesta." Did they shake hands at the end? Did they smile? Did they make nice for the camera? Yes, yes, yes. Did any of it look remotely genuine? Absolutely not.

How about "As the Best of Both Worlds Turn"?

Dogged by rumors they don't get along, R. Kelly and Jay-Z conveyed a tension onstage that seemed to fuel a "top that" contest at MCI Center.Jay-Z's sets at MCI Center may signify second thoughts on his retirement.