"The 15- and 16-year-olds really have been some of the biggest surprises," says Jennifer Lopez

Credit: Michael becker/FOX

American Idol is going to Vegas, baby!

The hit talent search brought 60 contestants – and its new panel of judges – to Sin City on Tuesday for a round of auditions. But in the town known as an adults-only playground, it was the youngest singers who shined.

“The 15- and 16-year-olds really have been some of the biggest surprises to us and the ones who have really blew us away,” Jennifer Lopez told reporters following rehearsals at The Mirage.

Randy Jackson agreed: “We never thought dropping the age one year, to 15 this year, would’ve made that big a difference,” he said. “But it’s crazy.” (The show lowered its minimum from age 16 for its 10th season.)

The Vegas stint comes after the show’s traditional Hollywood Week, when contestants already selected from seven other cities across America were winnowed down. And the cuts will continue, with only 40 set to return to Los Angeles.

“It’s proving very difficult to chop it down,” said Lopez, who proved to be a supportive judge in a new promo for the show. “We’re in that place where everybody’s so good, it’s like, ‘Who do we send home?’ It gets harder every day.”

The reason, according to Jackson, is that the singers are better than ever. “This is the best talent we’ve ever had,” he said.

But it’s not just the perfect voice they seek. “We’re looking for that ultimate idol in season 10,” Jackson continued. “[Someone who has] form, star power, unbelievable vocals – all of it, not just singers.”

This explains why the judges are being tough on some contestants. Except, who’ll be the toughest – in other words, who’s filling departed judge Simon Cowell‘s shoes?

[I’m] probably a little tougher than these two,” Jackson said in reference to Lopez and Steven Tyler. “This is my 10th season.”

Chimes in Tyler: “We’ve [all] been very hard. If they can’t sing, Randy will say, ‘Who told you you can sing?’ And I will ask them if they ate paint chips as a kid.”