City, who hold three games in hand of the leaders, cranked up the pressure by reducing the gap to six points with their 2-0 victory at Hull and the Blues duly cracked at Villa Park, ending the match with nine men and Mourinho in the stands as Fabian Delph netted the winner.
The result sees City come in from in from 13/8 to evens for the title while the current front-runners have drifted from 4/5 to 13/8 with Liverpool (11/2) and Arsenal (20/1).
Sky Bet's Head of Football Trading Paul Wiggins said: "We have granted Mourinho's wish of Chelsea no longer being considered title favourites after their defeat to Aston Villa, with the title firmly back in City's hands.
"Pellegrini's side have consistently attracted the most money for the title and winning at Hull despite playing with 10 men for 80 minutes was the perfect response to their cup losses.
"The fact they can now focus solely on the league should help their chances."
Meanwhile, at the other end of the table Fulham remain bottom but have had their relegation odds halved after beating Newcastle 1-0.
The Cottagers are now 2/7 second favourites for the drop with Cardiff shortening to 1/4 following their last-gasp 2-1 defeat at Everton.
Norwich were the other side to lose out, coming in from 12/5 to 7/4 following a 3-2 defeat at Southampton.
Crystal Palace are third favourites for the drop at 13/8 despite maintaining a three-point gap between themselves and Sunderland (7/4) with a 0-0 draw at the Stadium of Light.
West Brom are out to 3/1 after securing their first Premier League win under Pepe Mel, with their 2-1 victory at the Liberty Stadium seeing Swansea cut to 10/1.