McGoldrick scored twice inside four first-half minutes - his fourth and fifth of the season - to give Ipswich a 2-0 win and lift them into the Sky Bet Championship's top 10.
Brighton had no answer after McGoldrick's quick-fire brace and seeing a golden chance wasted by midfielder Andrew Crofts with the scores goalless.
Garcia, who was left fuming after referee Stephen Martin waved away second-half appeals for a penalty when Will Buckley's shot hit Tommy Smith's arm, believed McGoldrick was the big difference at Portman Road.
The Brighton boss said: "We knew McGoldrick could be a threat and today he showed that he is a player who can play at a higher level. He was the difference between the two sides.
"I'm not sure why the referee did not award a penalty in the second half - it was a clear handball. We were not good in the first 25 minutes, but after that we improved."
After Crofts' failure to hit the target from 10 yards, McGoldrick took little time in continuing his excellent start to the season.
He broke the deadlock on 20 minutes when his shot deflected off Keith Andrews and nestled into the top corner past the stranded Tomasz Kuszczak.
But there was nothing fortuitous about the second. McGoldrick picked up Daryl Murphy's flick header, turned Gordon Greer inside out and then drilled a low left-footed shot into the far corner.
Town boss Mick McCarthy, who described Crofts' miss as a "sitter", said: "We had to work very hard to beat a good side. You don't get anything easy from Brighton -they have some good players and actually started better than us.
"That's this league. We took our chances when they came along with a very good performance from Didds (McGoldrick). He was excellent today.
"You have to play well to beat a good side. Throughout the team, we had good performances. We mark the players after the game and you have to have seven out of tens rather than fours."
Brighton were unusually wasteful in possession and struggled to create any clear-cut chances, while McGoldrick almost completed his hat-trick but was unable to hit the target following incisive build-up play from Ryan Tunnicliffe and Murphy.
McGoldrick said: "I have had better days but I am delighted to score two goals and win.
"I have scored five in nine and I think I am getting better, but I just have to keep it up."