Any fights that you can think of where a fighter (either a washed up former champion, gatekeeper, or a journeyman) with 10 or more losses who unexpectedly beats a young undefeated fighter? The first that comes to mind is Orlando Salido vs. Juanma Lopez, although that seems a bit too recent.
Doesn't quite match your criteria of (either a washed up former champion, gatekeeper, or a journeyman) but I don't think Salido does either. Chucho Castillo had 10 losses on his ledger when he stopped Ruben Olivares.
My first thought was Emanuel Augustus & he has rightly stolen three 0´s with 10 losses on his own record. Where they were unexpected or not i don´t really know. one that surely qualifies is: 1997-01-11 Nashville Arena, Nashville, Tennessee, United States Fred Ladd 39-0 Loose KO1 vs Harold Bennet 16-16-2
Jesse Ferguson had 16 losses when he beat 18-0 Bobby Harris, Maurice Harris had about 12 losses when he KO'd Sergey Lehovich (spelling) I think the Russian was about 16-0. Kelvin Seabrooks had about 13 losses when he beat undefeated Louis Curtis and Thierry Jacob.