Blake Shelton's set at Country Jam in Colorado was punctuated by an appearance from girlfriend Gwen Stefani, but there was plenty to enjoy prior to their adorable duet. The singer and birthday boy played for nearly two hours, stopping frequently to tease his fans.

Shelton's age was the topic of many of his jokes. At first he confessed to being just 39, then 36, 34 ... 32. Shelton is actually 40 years old as of Saturday (June 18). Finally, he fessed up, saying, “Y’all have been so freakin’ nice to me on my 40th birthday."

"Neon Light" opened a set scheduled for just 90 minutes, and one song later Shelton began his tongue-in-cheek antagonizing.

"It's my birthday, start acting like it!" he shouted.

"All About Tonight," "Doin' What She Likes," "Mine Will Be You" and "Some Beach followed. Between songs fans attempted to sing "Happy Birthday" in unison. The result was the lyrics being tossed around like a beach ball. Shelton was sure to make fun of them for it.

His playful criticism of his audience is unique. After urging them to sing along to duets like "Lonely Tonight" and "My Eyes," he gave an honest review of the crowd's performance. "It's just the sound, literally the sound of your voices," he said, trying to pinpoint the issue, "It's kind of nasally." Fans who've seen him before recognized the patter and knew "Hillbilly Bone" would follow.

A quieter moment that during previous shows featured "The Baby" began with "Austin," but then evolved into "Go Ahead and Break My Heart," Shelton's song with Stefani. When she strode to the stage the tens of thousands at Country Jam erupted. Mostly the two kept their distance from one another while singing, but finally at the end they embraced at center stage, even sharing a kiss as she walked off.

Following up that moment wasn't easy. Two recent hits and "Home" with an amphitheater full of lit cell phone lights bled into "Honey Bee." Shelton will never match the energy of his opener Big & Rich, and he doesn't try. Quick wit, copious references to how much he wants to drink and one of the smoothest voices in country music replace running and dancing. He was one of few Country Jam artists not to struggle with the dry Colorado air. Each song sounded like the record.

His encore started with "Footloose," a song he covered for the rebooted movie's soundtrack. Then Stefani fired up the crowd with No Doubt's "Hella Good" before the country star returned to close with "God Gave Me You." The ballad was a peculiar choice to end with, especially after Stefani's electric solo spot onstage. The fans appreciated having the chance to sing along as they filed out, however.

Watch Blake and Gwen Sing Together at Country Jam

See Pictures of Blake Shelton Through the Years