Nemanja Matic’s strike and Paul Pogba’s brace rendered Mathias Jorgensen’s 88th-minute effort a mere consolation as they extended their losing run to six games.
The 26-year-old who endured a torrid time last season owing to a lingering ankle injury made his fifth appearance and first start since September in the tie.
However, despite putting in a decent shift in the encounter for the 57 minutes he featured, the Congo DR international could not prevent his side from suffering their 13th defeat this season.
"I think we played a good game and had our chances to go 1-0 up and even 1-1. We have to take the positives out of this game and move on,” Kachunga told club website.
"Everyone has to work on putting the ball in the net and to have a good feeling on the pitch. It could've been a different game if we went 1-0 up.
“We create the chances, now we just have to finish them.
"I was fighting for this club to give everything on the pitch. I am happy that I am back and that I played against Manchester United, and I hope I can help the team with my fighting spirit and everything that I have."
Huddersfield travel to Craven Cottage to take on Fulham on Saturday and the winger wants a quick positive response.
"This is English football; everything goes so quick. We now have a really important away game coming up, so we must recover and try everything,” he continued.
“Everyone saw today at 2-0 down that we were still trying to score, and everyone saw that our heads weren't down and that the players gave everything."
The defeat to Manchester United has left them with 10 points from 19 games and condemned them to the base of the league.