i think the shelby series 1 qualifies. some could argue reasonably that the corvette qualifies as well. the 1963 vette introduced independant rear suspension, was fuel injected and was well equipped to be competitive in road races. the 1957 vette with a radical duntov cam claimed to be the first car i believe to break 1HP / cu in. the first car though from my understanding was a 1956 chrysler 300B 354 hemi advertised at 355HP.
i would also argue that certain muscle cars though not luxurious like many exotics are indeed an american variation of exotic. they just didn't go around corners
. the shelby mustang gt350R (which did corner), the a990 mopars, ford thunderbolt, copo camaro's, dodge daytona, plymouth superbird, 429 boss mustangs (amongst others) all come to mind.
Jason