Two goals from Juan Mata secured a 2-1 victory in a game which will be remembered for Steven Gerrard???s red card 38 seconds after coming on as a substitute.
The win for the visitors moves fourth-placed United five points clear of Liverpool in fifth, and a further point ahead of Southampton and Tottenham ??? something which delights Van Gaal as well as a key victory over their historic rivals.
???It???s amazing for the fans because we have beaten Liverpool three times in one season,??? said the Dutchman.
???But also, in this moment, winning away here we now have a gap to positions five, six and seven, which is very important.???
United dominated the opening half an hour as they made life very difficult for a nervy Liverpool side, constantly putting pressure on the ball and dominating possession when they won it.
The hosts had spells of pressure before the break and initially reacted well after Gerrard???s red card before Daniel Sturridge pulled one back with 20 minutes remaining.
While pleased with the result, Van Gaal was disappointed his side didn???t keep up the intensity of the first 30 minutes, especially after Gerrard???s dismissal.
???I thought in the first half we played very well, maybe better than the first half against Tottenham,??? he added.
???But in the second half we didn???t play very well because, as always when you play against 10 men, a lot of players forget to press and also to dribble with the ball, so we have lots lost of unnecessary balls, and that brought Liverpool into the game.
???We forgot to press ??? in the first half with 11 against 11 and everybody knows what he has to do. In the second half most of the players are thinking ???the other player can do that???, and of course that???s not so good.
???In spite of the pressure from Liverpool we kept the ball and we could create a lot of possibilities ??? not big chances, but possibilities to score. I said in advance ???who can beat the pressure shall win???.???