Old Trafford is not too scary for the away team because we saw that the away team could easily beat manchester united at Old trafford. So with the previous defeat to Newcastle united, it is likely that Chelsea can try to win this match.
Looking at the two teams, in fact, they are equally sick. They're not in good form, so they equally have a chance. But with Man United's condition of playing home they have a better mentality. There are several percent of supporting factors that make Man United more passionate. But it was indeed the final week's win against Brighton. They won by a margin of 1 goal even with 10 players. In addition, Man United is currently in a bad condition. There are reports that Ten Hag is starting to be distrusted by the players. This is because Ten Hag is too rigid in coaching.
Yes these two teams are not in good form overall, and that means as you said equality makes both teams have the same chance, but maybe on the other hand I'm not entirely saying it's Chelsea, because lately they are quite consistent in giving surprises. Although in terms of standings statistics Manchester United are far above Chelsea but that is another thing, we can see how Chelsea have been playing lately, holding a draw against Manchester City and Arsenal is not an easy thing for most teams in the EPL, but Chelsea can do it, and I say it is not just luck, but indeed Pochettino seems to have managed to do something to his team even though it is not too prominent.
Another surprise is that even Chelsea can get the full three points despite only playing with 10 men in yesterday's match against Brighton who are now also standing above Chelsea in the table. I don't want to get into how Manchester United are doing, there's nothing I can say for the Red Devils other than "they're terrible this season", nothing to be hopeful about. So in conclusion it probably looks like I'll be betting on Chelsea in this one.