3 losses in a row

Lorenzo Boyd against future champions Taoufik Belbouli, Glenn McCrory and then Tommy Morrison .

Kimmuel Odem against Tony Tucker, Tommy Morrison and then Henry Akinwande

Pierre Coezter who fought Riddick Bowe, Frank Bruno then George Foreman in his last three.

Not quite as asked but Paulino Uzcuden against Primo Carnera, then a draw followed by a loss against Max Schmeling and then ran into Joe Louis. A tough run.

Also not quite as asked but Jose Ribalta against Tim Witherspoon, Bruce Seldon, then Pierre Coezter who obviously was not champion, but then onto Bruno followed by Michael Dokes. He also fought Tony Tubbs, Larry Holmes, Vitali Klitschko, Chris Byrd as well as Tyson. Quite the roster of champions as well as contenders throughout his career.