Justin Bieber kicked off his highly anticipated [article id="1685633"]Believe tour[/article] over the weekend, and the first night was certainly one to remember.

The 18-year-old star began his lengthy world tour in Phoenix, Arizona, on Saturday, where he shared a bit more with his plans than he had planned to. According to footage posted online, midway through swagging around to his track, "Out of Town Girl," the singer turned his body from the crowd and vomited. Bieber eventually finished out the performance, but not before leaving the stage twice and apologizing to fans.

Afterward the show, he tweeted about the incident, laughing it off in the style of "Anchorman" legend Ron Burgundy. "Milk was a bad choice! Lol," later adding, "Great show. Getting better for tomorrow's show."

Saturday night's show also had a more touching moment when Bieber paid tribute to his [article id="1694474"]late fan, Avalanna Routh[/article], known as Mrs. Bieber, who passed away last week after her lengthy battle with a rare brain cancer.

"Big day today. Tonight is for my angel. #mrsbieber" he wrote before taking the stage in Phoenix, where he later performed his song "One Less Lonely Girl" while images of the late fan flashed behind him. He later wrote, "Goodnight Avalanna. Tonight was for u. I love u."

After resting up, Bieber hit Las Vegas on Sunday, bringing his pal Usher along to hit the stage with him. "did it BIG in Vegas 2nite with big bro @UsherRaymondIV . Expect the Unexpected on the #BELIEVETOUR ..next stop....LOS ANGELES!! 2 NIGHTS!" he wrote.

Bieber has dates on his Believe tour slated for stops all across the globe right through May 2013.