Mind you that Chelsea are in tenth position and they have only 15 points from 11 games which is a poor return for a club like Chelsea, they have also won only 4 games in ths EPL this season. Spurs would never have lost that game, but they went two men down and had to play for over 40 minutes with just 9 players, they also had a couple of injuries to important players. I don't think Chelsea are resurgent, neither are they improving, and if their fans think they are flying right now, they'd be brought back to earth when they face City this Sunday.
However, Chelsea's victory at Spurs' home last week was undeniable luck and for any consistent team when faced with the situation of losing 2 players due to red cards, it would certainly be difficult to maintain their existing performance. Chelsea are still one of the worst teams this season and even though they managed to break into the top 10 of the standings, that won't be enough if they experience difficulties again in the next few matches. Pochettino must maintain the results obtained so far in order to be an additional value worth fighting for in the next match and if not it will be another lackluster result from Chelsea.
You could say that Chelsea success was just luck, I also see it that way and don't think that this victory will have an impact on their next match against Manchester City. Even though they will be playing at home, many doubt that Pochettino squad will be able to create a surprise by beating City. If luck will be on their side again that's a different story, but on paper I think Pep Guardiola squad deserves to be at the top.
Ups and downs in performance are a very natural thing, and Chelsea experienced difficult times when Pochettino took over as coach with more defeats. Chelsea have lost 18 points from 11 matches, and have a 12 point gap with City at the top of the standings. I assume they are just chasing tickets to the Europa League it seems, because that's the most realistic for now.