Who is the British singer/guitarist who performed in the original concert that spawned Derek & The Dominoes?

Question

It was originally called Eric & The Dynamos or something like that.
As I recall, the group was oringinally put together as just a one-off
performance, perhaps for a charity. A promoter or announcer mispronounced the name as Derek & The Dominoes and it stuck once the group was finalized.
Anyway, this particular guitarist didn't make it into the band as everyone came to know it but he was a big name in his own right and has been with a couple of major bands in addition to being a very successful solo artist.
The only hint I'll give you is that, in spite of being from England, he speaks with absolutely no hint of a British accent.
(I am remembering all of this 100% from my recollection of the original article in Rolling Stone when this first concert took place.)

No, Eric is Derek. Another guitarist and not Duane Allman. Thanks.

Answer 1

That would be Dave Mason.

Answer 2

Eric Patrick Clapp a.k.a Eric Clapton

Answer 3

Are you talking about Eric Clapton?