Considering the performances of both teams in the English Premier League this season, I think it's very safe to say that there's no much difference between the strength of both teams. We've seen Tottenham Hotspur go to Manchester City's home this season and delivered an incredible performance which earned them a 4:0 away win but for Chelsea, they've actually not been getting good results against the any of the big "6" clubs they've faced this season. Maybe Chelsea will finally get a win against a top side today but they'll have to do what they've never done against a top side to achieve that.
Looking at the record of meetings between Chelsea and Tottenham, it is clear that Chelsea is better. Even when their performance is not better than Tottenham, they can also get good results, it seems that Tottenham's headquarters are no longer that scary for Chelsea. However, this is still a record on paper and it is very possible that something different will happen on the field.
Tottenham this season has several problems that make them doubtful to be able to overcome Chelsea, especially since their meeting record favors Chelsea. If you look at that, I myself side with Chelsea in this match, but I also do not rule out the possibility that Tottenham can win the match.
Chelsea may have the edge over Tottenham based on record, but that doesn't mean they will be able to win against Tottenham this evening because this is a London derby so anything can happen. Tottenham is currently taking the lead but considering there is still a lot of time left I think Chelsea still has a chance to level but it's quite tough if they have to win because they were already 2 goals behind.