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

I saw the Eagles open for Ten Years After in the early 70's. I didn't much like them and the audience of TYA fans SURE didn't like them! 

On the other hand I saw Robin Trower open for Sha Na Na at Winterland in San Francisco in about 1974, and poor Sha Na Na. The place just went nuts for Trower and called him back for 3 encores and would have had him play all night if he could; he conquered the rock community of SF.

About a year later, Robin headlined a Day on the Green at Oakland Stadium, with Peter Frampton and Fleetwood Mac among the supports! Obviously this was right before they broke big, but that was still cool... 

Stevie Wonder opening for the Rolling Stones on their 1972 tour. Stevie Wonder levitated the auditorium. 

Linda Ronstadt opened for Jackson Browne at the Seton Hall University Field House in 1973. Jackson's full band including David Lindley. Linda stayed and sang with Jackson. Tickets were $2.50!

I can't confirm this, but it's rumored that Keith Richards opened for Mozart on more than one occasion.

Quicksilver Messenger Service opened for Three Dog Night in Kansas City. Would have been around 1974?  A very interesting grouping/coupling.