Maybe to try and turn a painful memory into a positive one, I'd suggest the Troy Deeney game was the beginning of our glorious era. If we'd have gone up that season we wouldn't have ended up with several key pieces of the puzzle (Mahrez, things really clicking for Vardy) and it really lit a fire under the team in the following season.
The 4-2 home loss to Spurs to miss out on CL qualification again was the last chance to keep it going. That money might have helped a lot and without it the bill had come due. We did win the Charity Shield a few months later and had the Europa run so I'd consider it to be the 1-0 loss in Rome.