Eminem, Dr. Dre, Diddy Headline at Beats Music's Launch Party

Busta Rhymes, Nas, Ice Cube, Bone Thugz N Harmony and Beats co-founder Dr. Dre played hits at the hot-ticket party.

Beats Music welcomed its new streaming service with a splashy launch concert at the Belasco Theatre where guests like Eminem, Diddy, Mase, Busta Rhymes, Nas, Ice Cube, Bone Thugz N Harmony and Beats co-founder Dr. Dre himself all played their hits as part of a “live playlist.”

But, if you stayed to catch Carole King’s all-star finale of “I Feel The Earth Move” around 11:30 p.m at the MusiCares gala a few blocks away at the Los Angeles Convention Center, you probably missed it.

The hot-ticket party reached the over-capacity mark somewhere around the hour of 11:00 pm, which left luminaries like Live Nation CEO Michael Rapino and Queen Latifah waiting behind the velvet rope for longer than just the normal beat before being waved in by Beats principals, and dozens of others left shut out entirely.

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Beats Music president Ian Rogers was seen escorting a few guests inside, as was Hollywood producer Brian Grazer, whose power of the guest list seemed indeterminate beyond the fact that he’s arguably the most recognizable producer in town -- if not still one of its most influential.

Downstairs, there was a "backstage" area where they were filming B-roll and taking photos of the performers before they went on stage. Diddy held the fort down there, chatting with fellow rappers and followed by admirers. One unexpected fan was Grazer, who stood to the side looking desperate to say hello to Diddy before he swooped in to shake his hand and tell him how much he loves him, before the pair hugged it out.

Guests who were able to venture inside reported great star sightings (Pink, Drake) and even better star smellings (Paris Hilton was spotted in VIP blazing up a sizeable joint). And though the line-up was impressively star-studded and an impressive reunion of some of the late 90s’ greatest hip-hop collabs (Diddy and Mase doing “Feels So Good” and “All About The Benjamins!” Dre and Blackstreet, together again on “No Diggity!”), the technical aspects of the event left a bit to be desired. “For a headphones company, the sound was terrible!” one party-goer told Billboard afterward.

Among the surprise guests included Robert Kraft -- 72-year-old owner of the New England Patriots -- with his much younger, much taller girlfriend. The NFL icon was in good spirits despite his team's loss last week, and chatted about one of his most popular players, Rob Gronkowski.

Rap fans were rubbing their eyes at the parade of talent on-stage, which included The Pharcyde, Method Man and Redman praising the joys of herb, Bone Thugs-n-Harmony (“Can’t Give It Up”) and Nas, slick in a sharkskin suit (“If I Ruled the World”).

While the main floor was banging, the upstairs balcony was where the VIPs hung out, with Pink spotted leaning over for a better view and Paul McCartney enjoying the show.

By the time Eminem finished performing three of his hits for the grand finale at half-past midnight, the three-and-a-half-hour party had wrapped, and execs like Beats creative officer Trent Reznor, Interscope’s Steve Berman, WME’s Marc Geiger, Atlantic’s Julie Greenwald, Glassnote’s Daniel Glass, Coke’s Joe Belliotti and many others began spilling out. But those who got in certainly left with a lasting impression of the show itself -- even if the music service being promoted became almost an afterthought. “That’s going to be hard to top,” WME’s Geiger was heard saying to a friend on his way out.

THR's Debbie Emery and Roy Trakin contributed to this article.