It was a back to back seven day stand at Harrah's Tahoe that made front page news in Billboard Magazine. First John Denver performed his sunshiney ecological love songs for the dinner show. Then the casino cleared the room. Then Frank Sinatra performed his boozy love songs at a midnight show for the scotch crowd. Tickets for both shows were $40. There was some speculation the two would perform together but never did.
Sinatra did make a quip about his clean cut counterpart:
A star is born in the nightclub field. I may have to teach him to drink and fool around...by the time I get to Denver he'll be Sicilian.
Two years later they did perform together on the 1977 Sinatra and Friends TV special.