10/15/2013 at 03:00 PM EDT
celebrated his 35th birthday Monday night at Los Angeles hot spot Bootsy Bellows.
Joined by friends Sean "Diddy" Combs, Justin Bieber
, Sugar Ray Leonard, Ashley Benson, Jermaine Dupri, T.I., Blake Shelton
, David Arquette, Miguel and Cassie, the R&B star arrived at the surprise bash around 11 p.m., and he was ready to party.
Dressed in a blue button-down, blue pants, pony-hair camouflage sneakers and a Gucci fedora, the birthday boy dominated the dance floor, according to onlookers.
"Usher was on the dance floor almost all night. He shared the floor with Diddy and Jermaine, who also danced almost all night long. Even David Arquette showed off his break-dancing skills," says a source.
At one point, Usher, Diddy and Bieber had a dance-off, and, our insider adds, "The crowd was going nuts."
The racy theme of the night was "S&M Cirque du Soleil," complete with girls dancing in plastic balls, plus whips and chains.
For dessert, guests indulged in a cake shaped like a boxing ring – and brought in by a string of scantily clad women who carried sparklers as they sung "Happy Birthday."
But Usher wasn't distracted by the ladies. "He was with his best friends, and there was a lot of love there," the source adds. "Everybody was so happy. There were so many celebratory hugs. It was such a fun night."
– Raha Lewis