Second-half headers from Tommy Smith and Daryl Murphy reduced the gap between eighth-placed Brighton and ninth-placed Ipswich to only two points and Town are now five points adrift of a play-off place.
Ipswich must play crucial games against Derby and Nottingham Forest in the next week and McCarthy said: "It's lovely to have a chance.
"We'll know more by the end of the week. I thought the squad was good at the start of the season and we wanted to make progress."
McCarthy was delighted with the way his side responded after conceding what he described as "poor goals" in their previous 3-1 home defeat at Wigan.
He added: "We did the right things, took our chances and it was a huge win. It's a difficult place to come. Brighton are a good side in the way they play out from the back and play good football."
Asked about his side's play-off prospects, McCarthy added: "We've still got a chance. We've now got to play Derby and Nottingham Forest and we'll know more by the end of the week."
Ipswich now boast two wins over Brighton this season with four goals scored and none conceded and McCarthy admitted: "I've no idea what the secret is. We've had to play well in both games."
Brighton went into the game with 17 clean sheets and the best defensive record in the Championship and head coach Oscar Garcia was dismayed at the manner in which his men "switched off" for both of Ipswich's goals.
The Spaniard said: "We had the best chances but didn't take them. We're frustrated and disappointed that we switched off twice and were punished.
"I'm happy with the performance but disappointed with the two goals conceded because we switched off twice. They did very little to win this game."
Brighton had only lost one of their previous 11 home matches in all competitions and Garcia said it was especially galling to lose as they were "the better side."
He added: "Ipswich were the better side in our first meeting but we were in this one."
Garcia rejected criticism directed by some fans that Albion are not ambitious enough in their home games, and said: "Anyone saying that we didn't create enough chances hasn't been at the game.
"I don't look at the table but we have a game at Sheffield Wednesday on Tuesday and we're looking forward to getting back to winning ways.
"We created more than enough chances to win the game but we didn't take them so we have to learn, improve on some things and move on."