A triple bill: Little River Band, Heart and the Eagles. Little River Band was better than the next two put together.
When the Eagles first broke up, Glenn Frey played with Little River Band. When I saw them in 2015, they were good.
A few years ago, we went to see Trombone Shorty at the Zoo Amphitheater here in Portland. His opening act was Robert Randolph and the Family Band. Now, Shorty puts on a good concert, and this was no exception, but Randolph blew the (non-existent) roof off the place. Holy crap, what a showman and musician.
This is what I love about The Dope. I made an innocuous post just to add to the post count and here comes digs and restores a chunk of my sorry memory. Thanks, digs! Any chance of replacing all that Algebra I lost? 
Time to check out Show of Hands.
I didn’t attend, but I distinctly remember ZZ Top opening for Billy Squier back in the 1980s.
A close friend kept wanting to go see Stevie Nicks in concert. The only two times I acquiesced were when the opening acts were Peter Frampton and Joe Walsh. Both were far better than the rest of the concert.
The clip of that performance has recently been restored and it’s glorious: A Quick One While He’s Away
Back in the 70’s I had a roommate who said he’d been to an Aerosmith concert, around the time that “Dream On” was a huge hit. The opening act was some group nobody had heard of at the time called Blue Oyster Cult. He said BOC opened with this number and kept going. Aerosmith sounded diminuitive and low-energy when they came on.
The Los Angeles date for 1983’s ARMS Concert was structured that way. All thee Yardbird guitarists played sets. Clapton led off and blew everybody else off-stage. It helped that Joe Cocker was doing some vocals and Bill Wyman and Ray Cooper were anchoring the rhythm section. They were followed by Jeff Beck doing all jazz-fusion crap and Jimmy Page playing with just a bass player. The place didn’t rock again until Eric and Jeff joined in on the end of “Stairway” and then, with maybe a two-second pause, launched into “Layla.” At that point I could have died happy. 
In 1973, I saw ZZ Top open for Quicksilver. We’d never heard of ZZ Top before, but they blew Quicksilver away!
I had a friend in college who was a huge Red Hot Chili Peppers fan, so when we heard they were coming to our little 3000 seat campus auditorium we camped out for tickets. There were two opening acts. I’d heard of one a little, the other not at all.
Which is how I saw Pearl Jam and Smashing Pumpkins open for RHCP. Literally about a week before Ten exploded. Both bands were really great.
Thing is, I have no idea if they upstaged the Chili Peppers or not, as RHCP didn’t even play a whole set. Somewhere around the 2nd or 3rd song some guy climbed on stage and security ruthlessly stomped the poor dude, tossing him off of the stage back into the auditorium’s fixed seating. Kiedis stops the band and calls out security, going on a pretty lengthy rant. In the middle of all this one of the other Peppers (I think it was the drummer) screams, “Everyone rush the stage!” Almost everyone did. The show ended in chaos.
As I walked out I passed right by Eddie Vedder who was chatting up two coeds and gave him a high-five. He’s pretty short.
Metallica routinely upstaged headlining bands throughout the 80s.
U2’s “PopMart Tour” in 97-98 had their first 9 shows opened by an obscure LA band called Rage Against the Machine. Rage did what Rage does, while U2 would then follow with an under-rehearsed set in front of an elaborate, malfunctioning stage setup.
Wow, I just looked this concert up. It was Tuesday, November 26, 1991. So 28 years ago to the day! What a coincidence!
I saw The Dickies open for a venerated punk act that everyone else had come to see, UK Subs. The Dickies killed it and the rest of the show was forgettable and bland.
Possibly the classic example is the 1963 Roy Orbison/Beatles tour where the latter was supposed to be the support but ended up rivaling for the headline. Both acts were considered great; it came down to personal taste which was greater.
Perhaps Aerosmith needed more cowbell?
I was just re-reading my post and realized Rage had been active since the early 90s and were globally-known by the time they opened on the U2 tour. They still upstaged U2, though.
Barely a footnote to this thread, but there’s a nice story.
In 1979 Rockpile toured with Lew Lewis Reformer as support. Lew was OK - and that was more than enough to upstage Rockpile - yeah, Dave Edmunds, Nick Lowe and all. A sleepfest.
Anyway, Lew blew a mean harmonica, something which will always make me happy. But rarely, if ever, have I see someone so pissed (meaning drunk) on stage. He was draped over the mike, surrounded by pints of beer stood on the stage by his feet. Between songs he would drink, and amuse himself by tossing one of his many harps up in the air and catching it - until he missed one which, with unerring accuracy, plunged into a pint glass like an Olympic diver, making barely a ripple on entry.
There then followed the marvelous spectacle of Lew being utterly unable to figure out what had just happened and where his harp had gone; searching the stage for it, with the crowd shouting In your pint! When he eventually he realised what the crowd was shouting, he then had to inspect each pint in turn to find the missing harp, before success and* considerable* cheering from the audience.
That one moment was plenty enough to upstage Rockpile. Who would have thought.
j
Heh! I think this was pre-cowbell Blue Oyster Cult.
- Flo & Eddie stole the show from Loggins and Messina. IMO etc.