What do you get when you bring together two guys known for their incredible guitar skills? A 'CMT Crossroads' show featuring Keith Urban and John Mayer! The two traded vocals and licks on each other's songs during the taping of an upcoming episode of the musical series, set to air later this year.

The invitation-only event was at standing room only, and the ones in their seats barely sat down throughout the night, watching the two musicians have even more fun with each other than the crowd was having, if that's possible. They kicked off the show with Keith's 'If Ever I Could Love,' an album cut picked by John from Keith's 'Defying Gravity,' then ran through 'Til Summer Comes Around,' 'Tonight I Wanna Cry' and 'Sweet Thing.' After a band change, they performed a handful of John's songs including 'Perfectly Lonely,' after which he said, "It's not every day you get Keith Urban to play on your tunes. I'm enjoying the hell out of this." Then the pair performed 'Slow Dancing in a Burning Room,' 'Say' and 'Gravity.' Keith and John then had some fun with dueling guitars and vocals on a smoking cover of George Michael's 'Faith' before they paid tribute to each other and called it a night.

While they were waiting on stage between songs for the TV crew to re-set, they did an impromptu jam of 'Folsom Prison Blues,' and at one point, while getting makeup touches, played around with their axes on the theme to 'Pink Panther.' John explained that it was a thrill to play with another guitar player who cares about 'pickups and what kind of wood is on the neck' of a guitar. Later, after moaning about why they didn't get together sooner, the pop star said they were basically cut from the same cloth. Keith said he was first introduced to the Connecticut native's music when he was out on tour with Brooks & Dunn and listened to his 2001 debut album, 'Room for Squares.'

In the wee hours of the morning following the taping, the 'Your Body is a Wonderland' singer took to his Twitter and wrote, 'Another fit of gratitude for my life as a musician. Thanks to my fans and an incredible night with Keith Urban. THAT guy ...'

A few special guests attended the show. Spotted in the crowd enjoying the music were Taylor Swift, Kix Brooks, Jake Owen and Love and Theft's Eric Gunderson.

This wasn't the first time these two took part in the 'CMT Crossroads' series. Previously, Keith was paired with rock legend John Fogerty, while Mayer performed with another country guitar hero, Brad Paisley.