We knew he had it in him!

Justin Bieber had one heck of a time in Las Vegas last night as the pop star and his crew partied all night at music producer Mally Mall's house until the wee hours in the morning!

"Justin was acting like he was the sh*t," an X17 photographer said. "He thinks he's a baller. He's only 19 and he's acting like he's 25."

The Never Say Never singer wasn't with his rumored cocktail waitress girlfriend Jordan Ozuna but chose a flock of girls to accompany him this time around.

And when it seemed he was done for the night, the 19-year-old singer showed that he can hang with the big boys. "Bieber went back to his hotel at 6am with a huge entourage," the photog added. "He thinks he's the king of Vegas."

We can only wonder when the partying finally ended. Even a king needs his sleep!