LAS VEGAS -- For the first hour of Dierks Bentley's Saturday night (April 6) performance in Las Vegas concert, he encouraged the crowd to sing along. But then Sheryl Crow came out on stage. And everything changed.

After singing his first 10 songs, Bentley said he'd had a song in his head all day. He started singing a solo version of "Picture," Sheryl Crow's hit duet with Kid Rock from 2002. Then Crow walked out onto the outdoor stage, surprising the thousands of fans packed into the parking lot of the Orleans Arena.

Bentley kept going, singing Kid Rock's parts, and Crow sang hers. And when she did, Bentley shushed the crowd as if to say, "Be quiet, I want to hear her sing." The two obviously have a solid friendship and a great performance rapport because she stayed onstage to do one of her own hits -- "If It Makes You Happy" -- and Bentley joined her on that one, too.

Four songs later came surprise No. 2: Tim McGraw.

It was during Bentley's last song of the night, "Home," and McGraw came out to talk about Operation Homefront, the group that gives mortgage-free homes to wounded warriors. But then he hinted that maybe he and Bentley would tour together someday -- with one caveat.

"Dierks and I have been friends for a long time. But he makes me nervous, standing up here with him," McGraw said. "He's too damn good looking."

The rest of Bentley's show was packed with his own hits, some reinvented to let his appreciation for bluegrass shine.

"We took an old song of ours and put a little bluegrass in the middle of it," he said to introduce "Settle for a Slow Down."

He also took several opportunities to connect with the fans gathered at the front of the stage. No easy feat, since the stage was very high off the ground. So to fist bump and high five those fans, it meant Bentley had to lay down on the stage and let his arms dangle over the edge. Which is exactly what he did.

The Eli Young Band did an hour-long set before Bentley, filled with 11 songs and about that many stories. Frontman Mike Eli charmed the audience talking about how Southwest Airlines had lost his guitar, so he'd had to borrow one from Bentley, and then telling the fans that whatever their dreams are, just to keep dreaming them.

"When I was a kid, sitting on the couch watching the ACMs, I'd be telling mama that one day I was gonna do that," he said. "I did not know how difficult that would be. But I believe in faith. I believe in luck. And I believe in putting yourself in the right situation."

Before that, Hunter Hayes brought his own 10-song set to the masses. And he made sure to thank the ones who were there from Las Vegas and the ones who made the trip by car or plane to enjoy some country music. They were happy to oblige, too, when Hayes asked them to be his background vocalists.

"If any of you know any of the words to any of these songs," he said, "sing them at the top of your lungs, OK?"

The show also featured Lee Brice, Dustin Lynch, Kix Brooks and Love and Theft earlier in the day. And throughout the festival, Brooks and the ACM made several charitable donations to military organizations. And so when Hayes sang "Where We Left Off," the song he wrote for the film Act of Valor, he dedicated it to the men and women who are serving and who have served.

"We love you. We thank you. We pray for you," Hayes said.

The ACM Party for a Cause was one of several events leading up to Sunday night's ACM Awards. CBS will broadcast the show live from the MGM Grand Garden Arena.