Following a torrid time in the press and on social media, it was imperative that van Gaal and his side answered their many critics by putting on a performance that was more akin to a United side than had been witnessed last weekend against Southampton.
To do so, the manager made two changes to his starting XI by replacing the injured Darmian with Varela and he dropped Herrera to the bench in favour of Mata. Line up: De Gea, Borthwick-Jackson, Smalling, Blind, Varela, Schneiderlin, Fellaini, Mata, Lingard, Rooney and Martial.
Fellaini was once again van Gaal's preferred choice to partner Schneiderlin in midfield and it would be interesting to see if the Belgian would cause havoc to the Rams' defence or be the hindrance to his own side that he sometimes is.
Derby got the tie underway amid an electric atmosphere inside the iPro Stadium, with the away supporters numbering almost 5,500, once again in superb voice.
The opening exchanges belonged to United as they had an encouraging start by bossing the play and not allowing the home side anytime on the ball. In fact, Derby's first effort on goal came in the tenth minute when a shot from Christie was easily collected by De Gea.
Exactly the start United had hoped for. Now could they keep control of the game and hopefully find the second crucial goal to kill the tie off?
It could and should have been 2-0 when Martial collected a return pass from Mata, but his first touch was too heavy as he bore down in the area.
Eight minutes before half time the iPro Stadium erupted as Thorne levelled for the home side to make a dent in all the hard work United had put in. A goal totally against the run of play and one where Thorne controlled the through ball well before evading the United defenders and poking the ball past De Gea.
The Reds had a good shout for a penalty after Martial's tracker seemed to handle the ball inside the area while making a tackle on the United forward.
Cup tie well and truly on as it was all square at half-time and it was Derby who ended the half with their tails up after the equaliser had given them a new sense of belief.
United had done everything that was expected of them, but once again came unstuck in one moment of hesitation at the back that allowed the Rams back into the game. But it was Martial who had caused the most damage to Derby with his spirited attacks.
The question now would be how would the Red Devils react in the second half?
The away side got the second half started with no changes having been made by van Gaal and showed their intent by attacking from the off. The ever lively Martial made a run down the left and tried a cross come shot which evaded everybody.
Thrilling play as first Mata and Lingard combined well inside the area, then Martial found the ball tied up between his feet in the crowded area and was unable to get away a shot.
Derby was somehow hanging on as United poured forward seeking the second goal with Varela providing the outlet down the right and Martial doing the business on the left with Lingard and Mata utilising their pace and guile respectively.
Close attention still had to be paid to Derby's attacks and full concentration would be needed for the last twenty minutes of the tie.
Van Gaal made his first change of the match by replacing the impressive Schneiderlin with the fit again Carrick.
The goal was Mata's last kick of the game as he made way for his compatriot Herrera, who would add fresh legs to the side for the final few minutes of the game.
The game was over as a competition following Mata's decisive strike, but still Derby didn't give up hope of salvaging some pride and if it hadn't been for a couple of errant shots they could have.
The star of the show was Anthony Martial who gave the home defence a merry dance every time he attacked and his footwork and vision is a wonderful thing to witness in a player so young. The good news for United, but bad news for opposing teams, is that Martial will only get better and when he moves into the middle as the leading striker then the side will truly reap the benefits of his immense talent. It was just a shame he couldn't find the goal to put the icing on top of his endeavours.
So, United are the first side into the bag for the 5th round draw. Whisper it quietly but could this be the season to win back the old trophy?
Thanks for reading.