I was going to throw Luis Santana in there, but he managed to get the better of Terry Norris twice. He even got the job done quicker in their second fight. If you ignore that his moment of glory was a foul, Tomas Molinares has a one punch KO of Marlon Starling amidst a career of mediocrity.
I'm not too familiar with the guy, but Rolando Pascua's win against Chiquita is completely out of sync with anything else he achieved in his career.
Turpin trained at Gwrych Castle in Wales and also owned the Great Orme complex but I'm not sure if he ever actually lived in Wales. I don't think Turpin can be viewed as a one fight wonder. He performed well in the rematch, although not as well as in the first fight, and came within seconds of beating Robinson again. Nobody beat Robinson twice until the 1960's by which time he was way, way past his prime.
THE classic "right place, right time" fighter. Nothing particularly impressive before Gomez, then beats the very faded Gomez, then goes straight downhill. Apparently he had drug issues, which apparently lead to his eventual murder.
Kirkland Laing outboxed near prime Roberto Duran back in 1982 and won quite handily. Considered a naturally talented fighter, whether because of inactivity, inconsistency, drug abuse etc. he could never quite put it all together again and have a successful run other than winning the British and EBU titles. Given his talent, he should've been contending at the world, not European level.
Billy Backus was not in the same class as Jose Napoles nor was Chucho Castillo in the same class as Ruben Olivares, IMO. Both won their titles on cuts. This is not meant to demean the performances of either Backus or Castillo, but they both were very fortunate to have "their nights of glory." Also, Lauro Salas, Paddy DeMarco, And Wallace (Bud) Smith were lucky enough to face the erratic Jimmy Carter in their title bouts. They all had short championship reigns. I bring up these examples to illustrate that "great" performances are often the result of happenstance and/or poor performances on the part of otherwise superior fighters.