Blake Shelton says Shakira and Usher started "jabbin' right off the bat" as soon as they sat in their The Voice judging chairs.
The pair join returning mentors Blake and Adam Levine on the hit US version of the singing contest, where each of the four judges gets a chance to pick their own contestants.
Blake says Shakira and Usher came prepared to compete from the beginning of the series.
"We figured out early on that this was no joke to those two. They came ready. They started jabbin' right off the bat when we got in the blind auditions. It was very obvious to Adam and I both that they had been paying attention and they knew what this show was all about," he told ET Online.
"I think things were cordial when we all first met... but Adam and I made a point not to try to help. The last thing you want to do is hand somebody a bullet for their gun in this competition."
Shakira and Usher replaced Christina Aguilera and Cee Lo Green as panellists on the TV talent competition.
The Columbian singer - who recently gave birth to her first child - says Blake and Adam have been hugely welcoming.
"Oh no, I'm not getting any advice from those guys. They're here to mislead me. They just want to get my contestants, especially my Latina girls," she quipped. "All jokes aside, these guys have been so great… Yeah, we compete, we try to beat each other and we joke all the time, but they've been so warm and so nice and such great hosts making Usher and I feel at home.”
"Blake and Adam made it very comfortable. They go back and forth; they play; they keep the energy very light, so it made it easy to slide in and even score talent at times," Usher added.