The best opening act you've ever seen & heard?

Rory Gallagher open for ZZ Top in 76

Steeley Dan opened for Rare Earth in 73

Cactus opened for Trapeze early 70’s

In the fall of 1968, I went to my first rock concert, at the Kinetic Playground in Chicago. We went to see Spirit, at the top of the bill, with two other acts.

The first act came on, and the lead singer was WEIRD AS HELL - with continuous convulsive body movements and a massive, fantastic voice. He was a complete unknown in the US at that time ... Joe Cocker and the Grease Band.

In 1969, we went to see Randy Newman performing solo at The Quiet Night in Chicago. The opening act was a couple of comics none of us had ever heard of. One guy was a burnout, the other was a Latino ... Cheech & Chong. Pretty damn funny. This was two years before they recorded their sketch that went viral on radio, "Dave's Not Here."

It was 1979 and I knew nothing about music.  I got tickets to see Eric Clapton in Providence at a Coliseum.  He was promoting the Slowhand album.  There was an opening act.  I asked a knowledgeable friend about them and he told me the opener had one famous song.  
 

It was Muddy Waters.  I wish I had paid him more attention. 

Two. Eagles opening for Linda Ronstadt and The Pretenders opening for The Rolling Stones.

In 1971 at the old Shady Grove Music Fair outside of DC in 1971 I went to see BJ Thomas, who was hot as hell at the time, and when five older African American guys took the stage to open the youngish crowd started murmuring. It was The Persuasions, and this was before a capella became a thing a decade or two later. An hour of gasps and cheers later came three encores because we'd forgotten all about who we'd come to see. To his credit, BJ showered them with praise as well instead of bitching about his very delayed start. Which I'd seen before (not from him). Years later at college in Arkansas I saw Styx open for I think Marty Robbins. That didn't go well. They were great but that was a southern 1979 crowd.