I use the game against Wolves on 29/12/18 at Wembley as the marker of the very start of the decline. We were so used to beating mid table teams at the time that when we went 2-1 down in the 83rd minute I couldn't believe I was watching Spurs as we looked finished. We had no fight left. Just couldn't raise our game, and even when we let the 3rd in there was no response at all.
That for me was the beginning of the end.
You know that season was so weird because we were winning matches quite regularly but we got lucky in quite a few of them, if you looked at the XG stats we were trending downwards in a lot of matches and the way we were playing wasn't sustainable. That of course was the Summer that killed us becuase of our self imposed transfer ban and we had players come back from the World Cup late and we had all that stadium delay bullshit as well, it's mental how we actually managed to finish top 4 that season.