The chance for Cheslea is about 50 percent according to the rates we can see but the chance for Aston Villa is 25 percent and this shows us that even if Cheslea doesn't win this game still Aston Villa can't have too much chance against this team.
Here are the updated rates for this match I think considering the weak performance of Chelsea and the unstable results they got, we can't try betting on a draw.

The difference in odds is quite significant and indeed, as the host, Chelsea is naturally the favorite. But just seeing the results that Chelsea got in the previous few matches made everyone sick and it was impossible for anyone to bet on their victory. Even last week against Bournemouth they only drew and I couldn't stop laughing at that result.
Well, however, the bet on Aston Villa winning is the most reasonable and I think Unai Emery's troops will win again by silencing Chelsea at Stamford Bridge after the last time they did it last April.
As big and attractive as the bookie's odds for Chelsea are, I think we all realize that this kind of thing doesn't work.
Chelsea's current condition cannot be predicted so it would be better to avoid any bets related to Chelsea. Currently they are still erratic and their performance still tends to decline which makes their matches unpredictable even if the opponent is a club below their level.
On the other hand, Aaton Villa for these 2 seasons in terms of performance I think is quite good and it is precisely in this match that Chelsea could not get points back.