The Hammers eased the pressure on Sam Allardyce after two heavy defeats by Nottingham Forest and Manchester City in the FA Cup and Capital One Cup respectively with a priceless win at the Cardiff City Stadium.
Goals from Carlton Cole and Mark Noble proved to be enough to give West Ham their first win in eight games and help lift them out of the bottom three at the expense of Cardiff.
"It is huge of course because we haven't won for a while and to come away from home and win 2-0 and keep a clean sheet, especially after the last two games when we conceded quite a few the confidence was low," McDonald told Sky Sports regarding the importance of the result.
"But we've picked them up after the Manchester City game, we've worked very, very hard on the training field, even though it has been a limited time, and we've had a few players back and I think it shows when the big players come back it gives us a chance to compete."
McDonald admitted the result was the perfect response to the critics who have been calling for the head of Allardyce after the heavy losses to Forest and Manchester City and praised the club's fans for sticking by the side.
"I think it is [the perfect response]. When you are not getting results obviously you come under pressure and people are asking questions why, but there is a huge boost today with winning 2-0, a huge boost with a couple coming back from injury and hopefully we will have another couple in the next couple of weeks.
"The support we've had over the last week, even though they haven't seen their team win today, I thought the crowd was absolutely fantastic, they stuck by their team and got behind their team, and hopefully they have gone home very happy after seeing a much-improved performance."
McDonald also revealed they were waiting to find out the extent of Guy Demel's injury after he was stretchered off following a clash with his own team-mate Roger Johnson.
Demel is thought to have suffered a suspected dislocated elbow as well as facial injuries to add to West Ham's lengthy injury list.
"He has taken a bad knock on his head and he has gone to hospital so we are just waiting on the doctor to come back to give us an idea on how he is, but I am sure he is in good hands," continued McDonald.
"I think it showed we have got players who put their body on the line which is great and we need to do that more often.
"And if we get a couple of injuries then it gives somebody else the chance to come in and, as long as we stick together and work hard for each other, then we will get our just rewards, just like we did today."