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Jason Derulo had enough on his mind when he joined Lady Gaga’s Monster Ball tour, his first major one, about two weeks ago. But then the 20-year-old “Whatcha Say” singer was told the crowds had been chewing up the opening acts and spitting them out.

“There were a lot of horror stories,” Derulo said Friday while sitting in his tour bus outside the Rosemont Theatre, where he performed with Gaga from Friday through Sunday. “The openers were having trouble because people were booing and chanting ‘Gaga’ during their performances. It was pretty bad.”

Kid Cudi was the main opener for Gaga but dropped out of the tour Dec. 16, saying he wanted to focus on recording music and his acting commitments. As a result, Derulo, who came aboard just before Cudi left and was supposed to play a 20-minute set, was given Cudi’s 30-minute time slot.

Derulo said he has managed to avoid the boos so far.

“I’ve gotten none of that,” he said. “The audience has been incredible. The fans have been yelling at the top of their lungs.”

How does Derulo’s stage setup compare to Gaga’s elaborate decor?

“Oh man, it’s very, very different,” he said, laughing. “She’s on this platform, while my stage is flat and regular. And I don’t have fog. I was planning for that stuff, but then I found out I couldn’t have it. I had to backtrack and think of more organic ways to get the crowd going.

“But my time is coming very soon.”

For more Luis, visit chicagotribune.com/aboutlastnight