"It was like I was on the tilt-a-whirl," he said.
Bryan pulled off a dizzying upset, all right, beating out the night's top winner Miranda Lambert, two-time entertainer of the year Taylor Swift and top male stars and good friends Blake Shelton and Jason Aldean for the academy's top award.
The 36-year-old Georgia native's reaction? He hugged the trophy and hung his head, appearing to fight back tears as members of the crowd at the MGM Grand shouted "Luke!"
"I don't think there was anyone in the room more shocked than him," Aldean said. "That's why I love him."
Though Bryan got tons of love before the ACMs because of his new role as co-host with Shelton, the idea of winning entertainer of the year was far from his mind as he prepared to replace Reba McEntire on the show. He told reporters afterward he was so focused on hosting duties, he had trouble remembering what categories he was nominated in.
And he didn't give himself any chance to beat Swift, the undeniable pop star who has reshaped the genre and used a legion of fans to rule the ACMs the last two years.
Heck, he was still opening for Aldean last summer and only recently started his own headline tour. Even he thought it was too early to win an award usually given as a reward to veteran performers who were almost universally acclaimed.
He won an award before the show, sharing vocal event of the year with Aldean and Eric Church for their collaboration on "The Only Way I Know." And he thought he might have a shot at album of the year or male vocalist.
"But this is unobtainable, this is so unobtainable," Bryan said as he held the trophy up and looked at it. "You know that statue in Rio De Janeiro (of Jesus Christ). That is what this award is like for me, up on the mount, you know."
Turns out a majority of a record 1.1 million voters thought he'd look good holding that silver trophy.
Bryan's win will be the talk of Las Vegas as the celebration continues well into Monday morning, but Lambert again walks away as the academy's trophy magnet.
She won her fourth straight female vocalist award, joining Reba McEntire and Loretta Lynn as the only singers to win female vocalist of the year four or more times. She also picked up three trophies for her hit song "Over You" — one for single record of the year and two for song of the year. She was performer of the song and co-wrote it with Shelton, her husband.
"As a songwriter, having your song and your lyrics recognized by your peers is pretty much as good as it gets," Lambert said. "And I'm so thankful for being in this genre of country music, every single time someone's nominated, I just cheer, because I love everybody to death. So thank you for accepting me as a songwriter, not just as a singer, because that means the world to me."
Church won two awards, including album of the year for "Chief," and was tied with Aldean, Little Big Town and Florida Georgia Line in overall win total. Church's producer, Jay Joyce, also won two awards — for album of the year and the off-camera producer of the year.
Church called "Chief," which was nominated two years in a row, a defining album.
"I think my career is going to be pre-'Chief' and post-'Chief,'" Church said. "Album of the year is most special to me."
Aldean, country's top-selling male act, also won male vocalist of the year. Little Big Town had wins for vocal group and video of the year. Florida Georgia Line won for new artist and were previous winners in the new vocal duo/group category. And husband and wife Shawna and Keifer Thompson continued their feel-good story as Thompson Square won its second straight vocal duo of the year award.
The night was full of colorful performances, but the anticipation of Garth Brooks and George Strait performing together overshadowed almost everything else. The two paid tribute to the late Dick Clark, the executive producer of the show since 1979 who passed away a year ago.
Brooks appeared on stage in flannel shirt and black cowboy hat with a Fu Manchu to perform his hit "The Dance" before Strait joined him for "The Cowboy Rides Away."
Reba McEntire introduced the two and paid tribute to Clark, momentarily breaking down as tears appeared in her eyes.
"He would slap me if he saw me crying up here," she said.
Shelton kicked the show off with his new single "Boys 'Round Here," a hip-hop-flavored ode to redneck swag. He was joined by Luke Bryan, Brad Paisley, Sheryl Crow and Pistol Annies, a trio that includes his wife Miranda Lambert.
Lady Antebellum debuted new song "Downtown" and Charles Kelley finished off the song by rubbing pregnant trio-mate Hillary Scott's belly. Carrie Underwood stepped out of a black Cadillac parked on stage as she started her song, "Two Black Cadillacs."
Lambert appeared later with a fiery, diamond-studded rendition of her recent hit "Mama's Broken Heart."
John Mayer joined Paisley for a guitar summit on "Beat This Summer" and Taylor Swift and Keith Urban joined Tim McGraw on stage for "Highway Don't Care," which Urban finished off with a scorching guitar solo.
And Stevie Wonder made his first appearance on a country music awards show, joining Hunter Hayes for a performance by two guys who got their start as precocious teens. Hayes kicked off their set with his song "I Want Crazy," then was joined by Wonder for his hit "Sir Duke." Wonder returned to finish off the show with "Signed, Sealed, Delivered."
Asked to explain why he decided to join Hayes on stage, he had a simple answer.
"What I can tell you is I have always been a lover of music and country music," Wonder said. "The amazing thing (is) I recently saw a few days ago a Motown show. And what was amazing to me, comparing this night to that, it was about lifting people up, lifting love up. And so tonight, again, here in this event, it's about lifting people up, music up, love up. Listen, we could not be here without love."
AP writer Hannah Dreier contributed to this report.