Van Gaal admitted his side did not deserve to win the contest, but believes the Red Devils are capable of overturning the deficit in the return leg of the Round of 16 tie at Old Trafford next week.
"You have to believe in everything, you have to believe we can create an atmosphere that Liverpool have done here at Anfield and then everything is possible," van Gaal said after goals either side of the break from Daniel Sturridge and Roberto Firmino condemned his side.
"Of course it is right, we did not create enough chances, I can not deny that. I don't think that we were very creative, but it was also the defence of Liverpool, and you can give the greatest credit to Liverpool.
"We have to improve a lot to score goals though, we know. I have seen that we did not cope with the high pressure of Liverpool, we could not cope and that created a great atmosphere in the stadium."