Bryce Alakai and Trinity Tatumwasted no time celebrating their “Love Island USA” victory after returning from Fiji … ’cause they marked the occasion with a star-studded dinner before Bryce kept the party going from behind the DJ booth.

Bryce’s manager, Eric Podwall, hosted the private celebration Wednesday night at The Bird Streets Club in West Hollywood, where about 20 guests gathered for a three-course tasting dinner on the members-only club’s private terrace.

The guest list included fellow “Love Island USA” stars Zach and Charlie Georgiou, Kayda Bosse, *NSYNC’s JC Chasez and his girlfriend Jennifer HuYoung, “Glee” stars Kevin McHale and Chris Colfer, Patrick Renna from “The Sandlot,” and several other cast members from the hit Peacock series.

After dinner, the celebration moved upstairs to the club’s rooftop lounge … and that’s when Bryce took over.

Folks who were there tell TMZ … Bryce plugged his own USB drive into the DJ booth and played music for roughly an hour and a half, turning the intimate dinner into a full-blown party.

For most of Bryce’s set, Trinity stayed by his side behind the DJ booth, but we’re told she eventually stepped away to hit the dance floor with Chris and JC.

We’re told JC and his girlfriend were dancing throughout the set, and before long the party grew beyond the original dinner guests as other club members joined the fun.

Bryce had the rooftop packed, with everyone dancing and celebrating the newly-crowned “Love Island USA” winners.

We’re told musician Henry Cornell got behind the piano during dinner, performing a string of songs that had guests gathering around for an impromptu sing-along to songs byBilly Joel.