Referee John Busby sent Eastmond off after consulting with fourth official Trevor Kettle, much to the bemusement of Sutton boss Matt Gray.
The Surrey club appealed against the decision to the Football Association, and on Tuesday revealed they had been successful.
A club statement read: "Following the red card shown to Craig Eastmond during Saturday's game against Northampton Town, we reviewed the video of the game and submitted an appeal to the FA.
"We have now received the outcome of that appeal, which we were delighted to learn was successul.
"In their response to us, the FA confirmed that 'from the evidence adduced the Regulatory Commission ruled that this was an instance of wrongful dismissal'."
The decisions means Eastmond will be available to play for Sutton in Tuesday night's Papa John's Trophy clash with Stevenage.
After the game, Sutton boss Gray said: "I'm standing close to the incident and I can hear the linesman talking to the referee on the mic and he hasn't even mentioned the tackle.
"The foul could have gone either way but I spoke to the referee at the end of the game and he says he hasn't seen anything and it was down to the fourth official.
"I spoke to their management team, who I respect and like, and they thought it was a red card, but I look at the reaction of all their players and the referee and it didn't seem one.
"I haven't seen it back. I will shortly but it looked harsh to me and I was surprised at the time."
It was not an opinion shared by Town boss Jon Brady, who said: ""It was 20 yards from me and the lad has gone over the ball with his studs and come down Mitch's shin.
"If you have any doubts, just look at Mitch's shin because he has a massive stud mark all the way down it. It's a red card and the right decision."