Hughes' reign as City boss came to an end in the immediate aftermath of the 4-3 win, with the club's Abu Dhabi-based owners announcing Roberto Mancini as his replacement.
In a statement issued by the League Managers' Association, Hughes said: "I was informed after Saturday's match against Sunderland that my contract with Manchester City was being terminated with immediate effect.
"Notwithstanding media coverage to the contrary, I was given no forewarning as to the club's decision.
"Given the speed with which my successor's appointment was announced, it would appear that the club had made its decision some considerable time ago."
Hughes added that he believed firmly that he had the club on target to achieve their pre-season expectations, with City lying in sixth place after just two league losses all season at the time of his sacking.
"I am extremely disappointed not to have been given the opportunity to see through my plans at the club," Hughes continued.
"At the beginning of the season I sat down with the owners and it was agreed that a realistic target for the season would be sixth place in the Barclays Premier League, or in the region of 70 points.
"All of this was communicated to the players and we all knew where we stood.
"Whilst everyone at the club would obviously have wanted to see more wins, we were absolutely on target at the time of my dismissal.
"I am very proud of the fact that I steered the club through the most significant period of change in its history," Hughes continued.
"I have always been aware of the responsibility that comes with being afforded the luxury of a significant transfer budget, and I was grateful that the club supported me with significant investment in players.
"I very much regret, however, that I will not now be able to enjoy the success that would undoubtedly have followed in the light of that investment.
"I believe that I have handled with dignity the recent pressure placed upon me by press speculation.
"I would like to thank the fans for their support throughout my time at the club and particularly at this difficult time, and I wish the club every success in the future, particularly in relation to the forthcoming Carling Cup semi-final, the club's first semi-final for 28 years."