Sometimes, a compatible key and a similar uptempo vibe are enough for a smooth segue. I discovered that this morning when iTunes shuffle mode faded out of The 5th Dimension's "Up, Up, And Away," and the Sara Watkins version of Willie Nelson's "I'm A Memory" began.
I'd imported the two CDs with those tracks at least a decade apart and had never thought to pair those songs up. Upon hearing that segue, however, I thought, "These songs were recorded in distinctly different eras and genres, and that makes the pairing sound even fresher." Their beats per minute are close enough to keep the momentum flowing, and the G minor key of "...Away" dovetails into "...Memory"'s G major key easily.
Just when I thought I'd heard every unlikely but successful segue I could possibly hear...